Methods for removing contaminants from aqueous solutions using photoelectrocatalytic oxidization

ABSTRACT

A photoelectrocatalytic oxidizing device having a photoanode being constructed from a conducting metal such as Ti as the support electrode. Alternatively, the photoanode is a composite electrode comprising a conducting metal such as Ti as the support electrode coated with a thin film of sintered nanoporous TiO 2 . The device is useful in methods for treating an aqueous solution such as groundwater, wastewater, drinking water, ballast water, aquarium water, and aquaculture water to reduce amounts of a contaminant. The method being directed at reducing the amount and concentration of contaminants in an aqueous solution comprising providing an aqueous solution comprising at least one contaminant, and, photoelectrocatalytically oxidizing the contaminant, wherein the contaminant is oxidized by a free radical produced by a photoanode constructed from an anatase polymorph of Ti, a rutile polymorph of Ti, or a nanoporous film of TiO 2 .

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to and benefit of U.S. patentapplication Ser. No. 12/369,219 filed Feb. 11, 2009, which claimspriority to and benefit of U.S. Provisional Patent Application Ser. No.61/027,622 filed Feb. 11, 2008, which is hereby incorporated herein byreference in its entirety.

This application is related to commonly-owned U.S. patent applicationSer. No. 11/932,741, which is hereby incorporated by reference.

This application is related to commonly-owned U.S. patent applicationSer. No. 11/932,519, which is hereby incorporated by reference.

STATEMENT REGARDING GOVERNMENT INTEREST

This invention was made with government support under 2007-33610-18003awarded by the USDA/CSREES. The United States Government has certainrights in the invention.

BACKGROUND OF THE DISCLOSURE

The present disclosure generally relates to the removal of contaminantsfrom aqueous solutions. Particularly, methods are disclosed for theremoval of organismal and chemical contaminants from aqueous solutionsincluding groundwater, wastewater, drinking water, aquaculture (e.g.,aquarium water and aquawater) and ballast water.

Water recirculation systems are expected to play a key role in theexpansion of aquaculture production in the United States because theyprovide year-round production of aquatic organisms under controlledconditions. Closed recirculation systems require little water and land,have minimal effluent discharge, and, can be constructed and operatedalmost anywhere including within cities close to major markets. Closedhatchery systems can also be operated in a biosecure manner unlike otherforms of aquaculture.

Fish sensitivity to ammonia and nitrite toxicity is a major factorlimiting expansion of an environmentally sustainable aquacultureindustry reliant on water recirculation technology. Closed recirculatingaquaculture systems provide year-round fish production under controlledconditions. Pond, net-pen and flow-through culture systems requiresignificantly more water and land. In contrast, very little water andland are needed for closed, recirculating aquaculture systems, whichalso yield minimal effluent discharge.

Closed, recirculating aquaculture systems may also be advantageouslyconstructed and operated in cities proximate to major markets. Atpresent, however, it is more cost effective to produce food fish inponds and other open systems due to the high cost of building andoperating complex biofiltration units, which are currently required foreffective recirculation systems.

Currently, however, recirculation aquaculture is generally unfavorableeconomically primarily because of the high costs of constructing andoperating the complex systems required for water circulation, solidscapture, oxygenation, and nitrogenous waste removal. Nitrogenous wasteremoval is particularly problematic. Numerous technological approacheshave been attempted to remove ammonia from recirculated water includingtrickle filters, rotating drums, and floating bead filters.

Disadvantages of biofilters include a high concentration of nitrates, acompromise between fish and bacteria for optimal growing conditions(e.g., temperature), and bacterial growth that clogs filter pores andreduces filtration efficiency. Cleaning of biofilters can also reducebacterial populations. New biofilters take 4-6 weeks to becomeoperational, and, for this reason, biofilters cannot be usedintermittently. Still other disadvantages include disturbances such asadding more fish or overfeeding fish that lead to spikes in ammonia, anddifficulty in treating sick fish with antibiotics which may also killbeneficial nitrifying bacteria populations on the biofilters.

Aquaria and recirculation aquaculture systems generally have few or noanoxic zones. Therefore, nitrates must be removed by periodic waterexchanges. Optimization is difficult because aquaculture biofiltrationsystems require good growing conditions for both the fish and bacteria.However, optimal temperatures for fish growth may be suboptimal fornitrifying bacteria. Existing biofiltration systems used in aquaria andother aquaculture systems have numerous other limitations. For example,autotrophic nitrifying bacteria and competing heterotrophic bacteriacolonize within biofilters clogging filter pores and reducingnitrification efficiency.

In general, sufficient nitrifying bacteria populations require around 6weeks to establish in new biofilters. Therefore, current systems cannotfilter intermittently. The filters must be operated even if there aretemporarily no fish in the system to maintain biofilter activity. Evenminor disturbances (such as tank cleaning, overfeeding, or adding newfish) can disrupt delicate nitrifying bacteria population equilibriumleading to ammonia spikes. Sick fish cannot be treated with antibioticsbecause antibiotics kill nitrifying bacteria.

Such limitations associated with biofiltration systems curtail theproduction of aquatic organisms in water reuse systems. Autotrophicnitrifying bacteria and heterotrophic bacteria can colonize thebiofilters, which clog filter pores and reduce the efficiency ofnitrification. Biofilters are difficult to clean without reducing thebeneficial bacterial populations. Nitrifying bacteria grow slowly takingweeks for sufficient populations of nitrifying bacteria to becomeestablished in new biofilters. Even minor disturbances, such as tankcleaning, overfeeding, or adding new fish, can disrupt the delicateequilibrium of the nitrifying bacteria populations leading to spikes inammonia. Nitrates accumulate in the water, which stimulates theproduction of nuisance algae. Nitrates can only be removed from theclosed system by periodic water exchange. Such problems increasemaintenance time and costs in all systems as well as salt disposalproblems associated with seawater systems.

Nitrogenous waste removal in open systems is particularly problematic.Numerous approaches have been investigated, including trickle filters,rotating drums, and floating bead filters. (Abeysinghe D et al., 1996,Biofilters for water reuse in aquaculture, Water Sci. Technol.34:253-260; deLosReyes A et al., 1996, Combination of a bead filter androtating biological contactor in a recirculating fish culture system,Aquacul. Eng. 15:27-39; Van Rijn J, 1996, The potential for integratedbiological treatment systems in recirculating fish culture-A review,Aquacul. 139:181-201; and, Malone Ret al., 2000, Use of floating beadfilters to recondition recirculating waters in warm water aquacultureproduction systems, Aquacul. Eng. 22:57-73).

Other methods for eliminating nitrogenous wastes utilize biologicalprocesses based on bacterial nitrification and de-nitrification. (CooperP et al., 1994, Process options for phosphorus and nitrogen removal fromwastewater, J. Inst. Water Environ. Manag. 8:84-92). Ammonia converts tonitrate using two types of aerobic autotrophic bacteria. One bacteriaoxidizes ammonia to nitrite (NO₂ ⁻), and the other converts nitrite tonitrate (NO₃ ⁻).

Under anoxic conditions, heterotrophic denitrifying bacteria reducenitrite and nitrate to nitrogen gas. Autotrophic ammonia-oxidizingbacteria are generally characterized by low growth rates and yields. Ingeneral, nitrification is the rate-limiting step in biological nitrogenremoval processes. Maintaining adequate levels of nitrifiers is asignificant problem in biological removal processes.

Nitrifiers and de-nitrifiers require different environmental conditionsfor growth. In wastewater treatment plants, total nitrogen removal iscommonly achieved using a two-stage system. Both steps can, however,occur simultaneously in a single reactor. (Helmer C et al., 1998,Simultaneous nitrification/denitrification in an aerobic system, WaterSci. Technol. 37:183-187).

Zebrafish rearing systems are used extensively in biomedical research.Bacterial metabolites associated with and produced by biofilters canadversely affect physiological responses of certified disease-free fishstrains. Thus, there is an absence or shortage of certified disease-freezebrafish.

Electrochemical oxidation has been an alternative approach to solvingthe ammonia removal problem. (Chen D, 2004, Electrochemical technologiesin wastewater treatment, Sep. Purif Technol. 38:11-41). Electrochemicaloxidation (as opposed to photoelectrochemical oxidation) is analternative approach to solving the ammonia removal problem. Suchmethods, which utilize electrodes and electrical potentials to oxidizenitrogenous compounds, are attractive because they can overcome many ofthe drawbacks of biological techniques. Electrochemical methods producelittle or no sludge, can work with high or variable pollutantconcentrations, and are generally unaffected by the presence ofimpurities.

Electrochemical oxidation systems and processes employ electrodes andelectrical potential to oxidize nitrogenous compounds. In principle,oxidation can be controlled by applying particular voltages. In thegeneral sequence of increasing voltages, ammonium is oxidized to higheroxidation states in the order of ammonium (NH₄ ⁺), nitrogen gas (N₂),nitrite (NO₂ ⁻) and nitrate (NO₃ ⁻). Ideally, one would like to oxidizeammonium to nitrogen gas which would then exit the system. However thishas not normally been possible using electrochemical systems.Electrochemical oxidation systems produce little or no sludge.Electrochemical oxidation systems also treat high and/or variablepollutant concentrations. Such systems are also substantially unaffectedby the presence of impurities. Use of an electrochemical oxidationprocess to remove 100% of ammonia (2600 mg/L) in a landfall leachate hasbeen reported. (Chiang L et al., 1995, Indirect oxidation effects inelectrochemical oxidation treatment of landfill leachate, Water Res.29:671-678).

During electrochemical oxidation, the concentration ratio HClO:N₂ and pHinfluence the production rate of chloramines such as NH₂Cl, NHCl₂ andNCl₃. The efficiency of ammonia oxidation through in situ production ofhypochlorite has been reported. (Lin S H et al., 1996, Electrochemicalremoval of nitrite and ammonia for aquaculture, Water Res. 30, 715-721;Lin S et al., 1997, Electrochemical nitrite and ammonia oxidation inseawater, J. Environ. Sci. Health, Part A A32:2125-2138).

However, several oxygen-containing anions are generated duringelectrochemical oxidation, such as SO₄ ²⁻, ClO₃ ⁻ and ClO₄ ⁻, and thesespecie inhibit the formation of ClO⁻ ions, which slows thedestruction/oxidation of ammonia. (Czarnetzki L et al., 1992, Formationof hypochlorite, chlorate and oxygen during NaCl electrolysis fromalkaline-solutions at a RuO₂/TiO₂ anode, J. Appl. Electrochem.22:315-324; and, Chiang H et al., 1996, Photodegradation of chlorinatedorganic wastes with N—TiO₂ promoted by P—CuO, J. Chinese Chem. Soc.43:21-27). When ammonia is chlorinated, final products may include toxicchlorine gas and explosive nitrogen trichloride. Moreover, theelectrochemical method may require high levels of energy, and chlorideions must be added to the system for the method to work. The electrodesmay also require titanium-based boron-doped diamond film electrodes(Ti/BDD) that demonstrate high activity and reasonable stability.However, such electrodes are very expensive. Other alternatives tobiological filtration, such as ammonia stripping and ion exchange, areimpractical or uneconomical in most circumstances.

In addition to nitrogenous wastes, various other contaminants have beenfound in aquacultures and other aqueous solutions such as groundwater.Groundwater pollution or contamination may be caused by human activitiessuch as application of fertilizers, herbicides, and pesticides to crops,and/or originate from industrial waste disposal, accidental spills,leaking fuel storage tanks, dumps and landfills. Large-scale use andleaking of underground fuel storage tanks, for example, has resulted ingroundwater contamination by gasoline and fuels. Additionally,groundwater contamination may occur naturally such as, for example, byarsenic.

Organisms may also contaminate water and aqueous environments and is oneof the world's largest health concerns. Organisms such as, for example,insects, nematodes, bacteria, protists (protozoa), and viruses maycontaminate water. Moreover, many of these organisms produce cysts thatmay exist in water. For example, Giardia can form cysts that survivefrom weeks to months in water from wells, water systems, and stagnantwater sources. These cysts may be resistant to conventional watertreatment methods.

Organisms and other wastes may also contaminate ballast water used inships for stability and trim. Once the ship arrives at its destinationit may release the ballast water into the new water. Subsequent releaseof the ballast water can result in the introduction of exotic andnon-native species and may cause detrimental impact on the environmentand local economy.

Various methods exist for removing contamination from aqueous solutions.Generally, for example, contaminants may be contained to prevent themfrom migrating from their source, removed, and immobilized ordetoxified.

Another method is to treat the aqueous solution at its point-of-use.Point-of-use water treatment refers to a variety of different watertreatment methods (physical, chemical and biological) for improvingwater quality for an intended use such as, for example, drinking,bathing, washing, irrigation, etc., at the point of consumption insteadof at a centralized location. Point-of-use treatment may include watertreatment at a more decentralized level such as a small community or ata household. A drastic alternative is to abandon use of the contaminatedaqueous solutions and use an alternative source.

Other methods are used for removing gasoline and fuel contaminants, andparticularly the gasoline additive, MTBE. These methods include, forexample, phytoremediation, soil vapor extraction, multiphase extraction,air sparging, membranes (reverse osmosis), and other technologies. Inaddition to high cost, some of these alternative remediationtechnologies result in the formation of other contaminants atconcentrations higher than their recommended limits. For example, mostoxidation methods of MTBE result in the formation of bromate ions higherthan its recommended limit of 10 μg/L in drinking water (Liang et al.,“Oxidation of MTBE by ozone and peroxone processes,” J. Am. Water WorksAssoc. 91:104 (1999)). A number of technologies have proven useful inreducing MTBE contamination, including photocatalytic degradation withUV light and titanium dioxide (Barreto et al., “Photocatalyticdegradation of methyl tert-butyl ether in TiO₂ slurries: a proposedreaction scheme,” Water Res. 29:1243-1248 (1995); Cater et al., UV/H₂O₂treatment of MTBE in contaminated water,” Environ. Sci Technol. 34:659(2000)), oxidation with UV and hydrogen peroxide (Chang and Young,“Kinetics of MTBE degradation and by-product formation duringUV/hydrogen peroxide water treatment,” Water Res. 34:2223 (2000); Stefanet al., Degradation pathways during the treatment of MTBE by the UV/H₂O₂process,” Environ. Sci. Technol. 34:650 (2000)), oxidation by ozone andperoxone (Liang et al., “Oxidation of MTBE by ozone and peroxoneprocesses,” J. Am. Water Works Assoc. 91:104 (1999)) and in situ and exsitu bioremediation (Bradley et al., “Aerobic mineralization of MTBE andtert-Butyl alcohol by stream bed sediment microorganisms,” Environ. Sci.Technol. 33:1877-1879 (1999)). Use of TiO₂ as a photocatalyst has beenshown to degrade a wide range of organic pollutants in water, includinghalogenated and aromatic hydrocarbons, nitrogen-containing heterocycliccompounds, hydrogen sulfide, surfactants, herbicides, and metalcomplexes (Matthews, “Photo-oxidation of organic material in aqueoussuspensions of titanium dioxide,” Water Res. 220:569 (1986); Matthews,“Kinetic of photocatalytic oxidation of organic solutions overtitanium-dioxide,” J. Catal. 113:549 (1987); Ollis et al., “Destructionof water contaminants,” Environ. Sci. Technol. 25:1522 (1991)).

Irradiation of a semiconductor photocatalyst, such as TiO₂, zinc oxide,or cadmium sulfide, with light energy equal to or greater than the bandgap energy (Ebg) causes electrons to shift from the valence band to theconduction band. If the ambient and surface conditions are correct, theexcited electron and hole pair can participate in oxidation-reductionreactions. The oxygen acts as an electron acceptor and forms hydrogenperoxide. The electron donors (i.e., contaminants) are oxidized eitherdirectly by valence band holes or indirectly by hydroxyl radicals(Hoffman et al., “Photocatalytic production of H₂O₂ and organic peroxideon quantum-sized semi-conductor colloids,” Environ. Sci. Technol. 28:776(1994)). Additionally, ethers can be degraded oxidatively using aphotocatalyst such as TiO₂ (Lichtin et al., “Photopromoted titaniumoxide-catalyzed oxidative decomposition of organic pollutants in waterand in the vapor phase,” Water Pollut. Res. J. Can. 27:203 (1992)). Areaction scheme for photocatalytically destroying MTBE using UV and TiO₂has been proposed, but photodegradation took place only in the presenceof catalyst, oxygen, and near UV irradiation and MTBE was converted toseveral intermediates (tertiary-butyl formate, tertiary-butyl alcohol,acetone, and alpha-hydroperoxy MTBE) before complete mineralization(Barreto et al. “Photocatalytic degradation of methyl tert-butyl etherin TiO₂ slurries: a proposed reaction scheme,” Water Res. 29:1243-1248(1995)).

Furthermore, the most commonly used method of treating aqueous solutionsfor disinfection of microorganisms is chemically treating the solutionwith chlorine. Disinfection with chlorine, however, has severaldisadvantages. For example, chlorine content must be regularlymonitored, formation of undesirable carcinogenic by-products may occur,chlorine has an unpleasant odor and taste, and requires the storage ofwater in a holding tank for a specific time period.

Accordingly, there is a need in the art for alternative approaches fortreating aqueous solutions to reduce amounts of contaminants.Specifically, it would be advantageous to have methods for treatingvarious aqueous solutions including groundwater, wastewater, drinkingwater, aquarium water, and aquaculture water to remove contaminantswithout the addition of chemical constituents, the production ofpotentially hazardous by-products, or the need for long-term storage.

SUMMARY OF THE DISCLOSURE

The present disclosure is generally directed to methods of treatingaqueous solutions to reduce amounts of contaminants. More specifically,one aspect of the invention is a photoelectrocatalytic compositephotoanode for removing contaminants from aqueous solutions. Thephotoanode comprises a solid nanoporous film member having a median porediameter in the range of 0.1-500 nanometers constructed from TiO₂nanoparticles, the nanoporous film member adhered to a conductivesupport member.

In an exemplary embodiment of the photoelectrocatalytic compositephotoanode, the median pore diameter is in the range of 0.3-25nanometers.

In another exemplary embodiment of the photoelectrocatalytic compositephotoanode, the median pore diameter is in the range of 0.3-10nanometers.

In another exemplary embodiment of the photoelectrocatalytic compositephotoanode, the nanoporous film member has an average thickness in therange of 1-2000 nm.

In another exemplary embodiment of the photoelectrocatalytic compositephotoanode, the nanoporous film member has an average thickness in therange of 5 to 500 nm.

In another exemplary embodiment of the photoelectrocatalytic compositephotoanode, the nanoporous film member is constructed from a stable,dispersed suspension comprising TiO₂ nanoparticles having a medianprimary particle diameter in the range of 1-50 nanometers. Thenanoporous film may also be deposited by other methods, such as plasma,chemical vapor deposition or electrochemical oxidation.

In another exemplary embodiment of the photoelectrocatalytic compositephotoanode, the TiO₂ nanoparticles have a median primary particlediameter in the range of 0.3-5 nanometers.

In another exemplary embodiment of the photoelectrocatalytic compositephotoanode, the nanoporous film member is constructed from a stable,dispersed suspension further comprising a doping agent.

In another exemplary embodiment of the photoelectrocatalytic compositephotoanode, the doping agent is Pt, Ni, Au, V, Sc, Y, Nb, Ta, Fe, Mn,Co, Ru, Rh, P, N or carbon.

In another exemplary embodiment of the photoelectrocatalytic compositephotoanode, the conductive support member is annealed titanium foil.Modifications of the titanium foil that improve photoanode performanceinclude making holes or perforations at regular intervals in the foil(about 0.5 cm to about 3 cm spacing between the holes), and corrugatingthe foil to produce a regular wave-like pattern on the foil surface. Theheight of a corrugation “wave” is about 1 mm to about 5 mm. Otherconductive supports may be employed, such as conductive carbon or glass.

In another exemplary embodiment of the photoelectrocatalytic compositephotoanode, the nanoporous film member is constructed by applying astable, dispersed suspension having TiO₂ nanoparticles suspendedtherein, and, the TiO₂ nanoparticles are sintered at a temperature inthe range of 300° C. to 1000° C. for 0.5 to 10 hours to produce thenanoporous film member.

In another exemplary embodiment of the photoelectrocatalytic compositephotoanode, the stable, dispersed suspension is made by reactingtitanium isopropoxide and nitric acid in the presence of ultrapure wateror water purified by reverse osmosis, ion exchange, and one or morecarbon columns.

In another exemplary embodiment of the photoelectrocatalytic compositephotoanode, the photoelectrocatalytic composite photoanode iscylindrical in shape.

Another aspect of the invention is a photoelectrocatalytic oxidationdevice for use in an aquarium or aquaculture comprising any one of theabove photoelectrocatalytic composite photoanodes, a cathode, a housingmember having an inlet and outlet adapted to house the anode andcathode, a light source assembly adapted to emit ultraviolet light tothe photoelectrocatalytic composite photoanode, and, an electrical powersource adapted to apply a voltage across the photoelectrocatalyticcomposite photoanode and cathode in the range of −1 V to +12 V.

In an exemplary embodiment of the photoelectrocatalytic oxidationdevice, the cathode is constructed from Pt, Ti, Ni, Au, stainless steelor carbon.

In another exemplary embodiment of the photoelectrocatalytic oxidationdevice, the cathode is in the shape of a wire, plate or cylinder.

In another exemplary embodiment of the photoelectrocatalytic oxidationdevice, the device further comprises a reference electrode and a voltagecontrol device, such as a potentiostat, adapted to maintain a constantvoltage or constant current between the reference electrode and thephotoelectrocatalytic composite photoanode, whereby the housing memberis adapted to house the reference electrode.

In another exemplary embodiment of the photoelectrocatalytic oxidationdevice, the device further comprises a semi-micro saline bridge memberconnecting the potentiostat and reference electrode, whereby the housingmember is adapted to house the saline bridge.

In another exemplary embodiment of the photoelectrocatalytic oxidationdevice, the reference electrode is constructed from silver and is in theshape of a wire.

In another exemplary embodiment of the photoelectrocatalytic oxidationdevice, the device further comprises a carbon filter adapted to filterchlorine from the water, and, a computer adapted to send a controlledsignal to the existing power supplies to pulse the voltage and current.

In another exemplary embodiment of the photoelectrocatalytic oxidationdevice, the housing member is adapted to house the light source assemblyand the electrical power source is adapted to generate an electricalpotential in the range of 1.2 V to 3.5 V across thephotoelectrocatalytic composite photoanode and cathode (or, 0 to 2.3 Vvs the reference electrode).

Alternatively, the instant device may employ both constant currentand/or constant voltage between anode and cathode. The effective voltagerange may be in the range of −1 V to +12 V.

In another exemplary embodiment of the photoelectrocatalytic oxidationdevice, the light source assembly comprises a lamp or bulb and atransparent quartz or fused silica member adapted to house the lamp, andthe ultraviolet light has a wavelength in the range of 200-380 nm. Thedevice will also function using sunlight instead of the light sourceassembly.

In another exemplary embodiment of the photoelectrocatalytic oxidationdevice, the lamp is adapted to emit germicidal UVC or black light UVA.

In another exemplary embodiment of the photoelectrocatalytic oxidationdevice, the germicidal UVC emits a peak wavelength of 254 nm, and theblack light UVA emits a wavelength in the range of 300-380 nm.

In another exemplary embodiment o the photoelectrocatalytic oxidationdevice, the lamp is a low pressure mercury vapor lamp adapted to emit UVgermicidal irradiation at 254 nm wavelength.

In another exemplary embodiment of the photoelectrocatalytic oxidationdevice, the lamp is adapted to emit an irradiation intensity in therange of 1-500 mW/cm². The irradiation intensity varies considerablydepending on the type of lamp used. Higher intensities improve theperformance of the photoelectrocatalytic oxidation (PECO) device. Theintensity can get so high that the system is swamped and no furtherbenefit is obtained. That value depends upon the distance between thelight and the photoanode.

In another exemplary embodiment of the photoelectrocatalytic oxidationdevice, the light source assembly is disposed exterior to the housingmember, and the housing member further comprises a transparent memberadapted to permit ultraviolet light emitted from the light sourceassembly to irradiate the photoelectrocatalytic composite photoanode.

Another aspect of the invention is a method of reducing the amount andconcentration of ammonia in an aquarium or aquaculture comprising thesteps or acts of providing an aqueous solution comprising water, NH₃,NH₄ ⁺ and 1 ppb to 200 g/L NaCl, and, photoelectrocatalyticallyoxidizing the NH₃ and NH₄ ⁺ to produce N₂ gas, NO₂ ⁻ and NO₃ ⁻.

In an exemplary embodiment of the method of reducing the amount andconcentration of ammonia in an aquarium or aquaculture, the aqueoussolution has a pH in the range of 5 to 10.

In another exemplary embodiment of the method of reducing the amount andconcentration of ammonia in an aquarium or aquaculture, the aqueoussolution comprises 1 to 41 g/L NaCl.

In another exemplary embodiment of the method of reducing the amount andconcentration of ammonia in an aquarium or aquaculture, the aqueoussolution comprises in the range of 0.05 ppb to 9 ppm NH₃ and NH₄ ⁺ asnitrogen.

In another exemplary embodiment of the method of reducing the amount andconcentration of ammonia in an aquarium or aquaculture, NH₃ and NH₄ ⁺are photoelectrocatalytically oxidized using a voltage in the range of−1 V to +12 V.

In another exemplary embodiment of the method of reducing the amount andconcentration of ammonia in an aquarium or aquaculture, NH₃ and NH₄ ⁺are photoelectrocatalytically oxidized using a voltage in the range of1.2 to 3.5 V.

In another exemplary embodiment of the method of reducing the amount andconcentration of ammonia in an aquarium or aquaculture, NH₃ and NH₄ ⁺are photoelectrocatalytically oxidized using sunlight or ultravioletlight having a wavelength in the range of 200 to 380 nm.

In another exemplary embodiment of the method of reducing the amount andconcentration of ammonia in an aquarium or aquaculture, the ultravioletlight is germicidal UVC having a peak wavelength of 254 nm or blacklight UVA having a wavelength in the range of 300-380 nm.

Another aspect of the invention is an aquarium comprising a fish tankand any one of the above photoelectrocatalytic oxidation devices.

Another aspect of the invention is a photoelectrocatalytic uncoatedanode constructed from an anatase polymorph of Ti or a rutile polymorphof Ti.

In an exemplary embodiment of the photoelectrocatalytic uncoated anode,the uncoated anode is constructed from the rutile polymorph of Ti.

In another exemplary embodiment of the photoelectrocatalytic uncoatedanode, the rutile polymorph of Ti is constructed by heating an anatasepolymorph of Ti at a temperature in the range of 300° C. to 1000° C. fora sufficient time.

In another exemplary embodiment of the photoelectrocatalytic uncoatedanode, the anatase polymorph of Ti is heated at 500° C. to 600° C. toproduce the rutile polymorph of Ti.

In another exemplary embodiment of the photoelectrocatalytic uncoatedanode, the uncoated anode is configured as a foil, with or withoutperforations and corrugations.

In another exemplary embodiment of the photoelectrocatalytic uncoatedanode, the uncoated anode is further configured as cylindrical in shape.The foil conductive support member of the uncoated anode may be with orwithout perforations and corrugations.

Another aspect of the invention is a photoelectrocatalytic oxidationdevice for use in an aquarium or aquaculture comprising any one of theabove photoelectrocatalytic uncoated anodes, a cathode, a housing memberhaving an inlet and outlet adapted to house the uncoated anode andcathode, a light source assembly adapted to emit ultraviolet light tothe photoelectrocatalytic uncoated anode, and, an electrical powersource adapted to apply a voltage across the photoelectrocatalyticuncoated anode and cathode in the range of −1 to +12 V.

In an exemplary embodiment of the photoelectrocatalytic oxidationdevice, the cathode is constructed from Pt or Ti.

In another exemplary embodiment of the photoelectrocatalytic oxidationdevice, the cathode is constructed from Pt, Ti, Ni, stainless steel orcarbon, and the cathode is in the shape of a wire or a plate or acylinder.

In another exemplary embodiment of the photoelectrocatalytic oxidationdevice, the device further comprises a reference electrode and apotentiostat adapted to maintain a constant voltage between thereference electrode and the photoelectrocatalytic uncoated anode, andthe housing member is adapted to house the reference electrode.

In another exemplary embodiment of the photoelectrocatalytic oxidationdevice, the device further comprises a semi-micro saline bridge memberconnecting the potentiostat and reference electrode, and the housingmember is adapted to house the saline bridge.

In another exemplary embodiment of the photoelectrocatalytic oxidationdevice, the reference electrode is constructed from silver.

In another exemplary embodiment of the photoelectrocatalytic oxidationdevice, the reference electrode is in the shape of a wire.

In another exemplary embodiment of the photoelectrocatalytic oxidationdevice, the housing member is adapted to house the light sourceassembly, and the electrical power source is adapted to generate anelectrical potential in the range of 1.2 to 3.5 V across thephotoelectrocatalytic uncoated anode and cathode.

In another exemplary embodiment of the photoelectrocatalytic oxidationdevice, the light source assembly comprises a lamp or bulb and atransparent quartz or fused silica member adapted to house the lamp, andthe ultraviolet light has a wavelength in the range of 200-380 nm.

In another exemplary embodiment of the photoelectrocatalytic oxidationdevice, the lamp is adapted to emit germicidal UVC or black light UVA.

In another exemplary embodiment of the photoelectrocatalytic oxidationdevice, the germicidal UVC emits a peak wavelength of 254 nm, and theblack light UVA emits a wavelength in the range of 300-380 nm.

In another exemplary embodiment of the photoelectrocatalytic oxidationdevice, the lamp is a low pressure mercury vapor lamp adapted to emit UVgermicidal irradiation at 254 nm wavelength.

In another exemplary embodiment of the photoelectrocatalytic oxidationdevice, the lamp is adapted to emit an irradiation intensity in therange of 1-500 mW/cm².

In another exemplary embodiment of the photoelectrocatalytic oxidationdevice, the light source assembly is disposed exterior to the housingmember, and, the housing member further comprises a transparent memberadapted to permit ultraviolet light emitted from the light sourceassembly to irradiate the photoelectrocatalytic uncoated anode.

Another aspect of the invention is a method of reducing the amount andconcentration of ammonia in an aquarium or aquaculture comprising thesteps or acts of providing an aqueous solution comprising water, NH₃ andNH₄ ⁺ and 1 ppb to 200 g/L NaCl, and, photoelectrocatalyticallyoxidizing the NH₃ and NH₄ ⁺ to produce N₂ gas (as well as insignificantamounts of some by-products such as NO₂ ⁻ and NO₃ ⁻), wherein the NH₃and NH₄ ⁺ are oxidized on (or proximate to) the surface of a photoanodeconstructed from an anatase polymorph of Ti, a rutile polymorph of Ti,or a nanoporous film of TiO₂.

In an exemplary embodiment of the method of reducing the amount andconcentration of ammonia in an aquarium or aquaculture, the aqueoussolution has a pH in the range of 5 to 10.

In another exemplary embodiment of the method of reducing the amount andconcentration of ammonia in an aquarium or aquaculture, the aqueoussolution comprises 1 to 41 g/L NaCl.

In another exemplary embodiment of the method of reducing the amount andconcentration of ammonia in an aquarium or aquaculture, the aqueoussolution comprises in the range of 0.05 ppb to 9 ppm NH₃ and NH₄ ⁺ asnitrogen.

In another exemplary embodiment of the method of reducing the amount andconcentration of ammonia in an aquarium or aquaculture, NH₃ and NH₄ ⁺are photoelectrocatalytically oxidized by a voltage in the range of −1 Vto +12 V.

In another exemplary embodiment of the method of reducing the amount andconcentration of ammonia in an aquarium or aquaculture, NH₃ and NH₄ ⁺are photoelectrocatalytically oxidized using a voltage in the range of1.2 to 3.5 V.

In another exemplary embodiment of the method of reducing the amount andconcentration of ammonia in an aquarium or aquaculture, NH₃ and NH₄ ⁺are photoelectrocatalytically oxidized using sunlight or ultravioletlight having a wavelength in the range of 200 to 380 nm.

In another exemplary embodiment of the method of reducing the amount andconcentration of ammonia in an aquarium or aquaculture, the ultravioletlight is germicidal UVC having a peak wavelength of 254 nm or blacklight UVA having a wavelength in the range of 300-380 nm.

Another aspect of the invention is a photoelectrocatalytic oxidationdevice for use in an aquarium or aquaculture comprising any one of thephotoelectrocatalytic composite photoanodes or uncoated anodes above, acathode, a housing member having an inlet and outlet adapted to housethe anode and cathode, and, an electrical power source adapted to applya voltage across the photoelectrocatalytic composite photoanode andcathode in the range of −1 V to +12 V, wherein the housing is adapted topermit sunlight to illuminate both the anode or a solar cell adapted toprovide the voltage applied across the photoelectrocatalytic compositephotoanode and cathode.

Another aspect of the invention is an aquarium containing a fish tankand any one of the above photoelectrocatalytic oxidation devices.

Another aspect of the invention is a closed, recirculating aquaculturesystem containing any one of the above photoelectrocatalytic oxidationdevices.

In another aspect, the present disclosure is directed to methods oftreating an aqueous solution having one or more contaminants therein toreduce the amounts of contaminants. The method comprises providing anaqueous solution comprising at least one contaminant selected from thegroup consisting of an organism, an organic chemical, an inorganicchemical, and combinations thereof and exposing the aqueous solution tophotoelectrocatalytic oxidization, wherein one or more contaminant isoxidized by a free radical produced by a photoanode, wherein thephotoanode comprises an anatase polymorph of titanium, a rutilepolymorph of titanium, or a nanoporous film of titanium dioxide.

In another aspect, the present disclosure is directed to methods ofenvironmental remediation, the method comprising providing a sample ofenvironmental medium comprising at least one contaminant selected fromthe group consisting of an organism, an organic chemical, an inorganicchemical, and combinations thereof and exposing the sample of anenvironmental medium to photoelectrocatalytic oxidization, wherein oneor more contaminant is oxidized by a free radical produced by aphotoanode, wherein the photoanode comprises an anatase polymorph oftitanium, a rutile polymorph of titanium, or a nanoporous film oftitanium dioxide.

In another aspect, the present disclosure is directed to methods oftreating an aqueous solution having one or more contaminants therein toreduce the amounts of contaminants. The method comprises providing anaqueous solution comprising at least one contaminant selected from thegroup consisting of an organism, an organic chemical, an inorganicchemical, and combinations thereof and exposing the aqueous solution tophotoelectrocatalytic oxidization, wherein one or more contaminant isoxidized by a chlorine atom produced by a photoanode, wherein thephotoanode comprises an anatase polymorph of titanium, a rutilepolymorph of titanium, or a nanoporous film of titanium dioxide.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be better understood, and features, aspects andadvantages other than those set forth above will become apparent whenconsideration is given to the following detailed description thereof.Such detailed description makes reference to the following drawings,wherein:

FIG. 1 is an electrochemical energy schematic graphically illustratingone embodiment of the photoelectrocatalytic oxidation (PECO) device ofthe instant invention showing oxidation of ammonia to nitrogen gas,whereby UV light of sufficient energy illuminates a photoanode includinga nanoporous titanium dioxide (TiO₂) photocatalyst film coated to a Tisupport, whereby electrons in the valence band (VB) are excited into theconduction band (CB) producing highly reactive electrons and holes thatpromote oxidation of ammonia on the anode surface, whereby thephotogenerated electrons preferentially flow to the cathode reducingprotons and producing hydrogen gas (H₂) and/or reducing oxygen gas (O₂)and producing water, whereby ΔG_(a) is the minimum energy required forthe activation of NH₃, whereby ΔG_(cell) is the maximum energy obtainedby the device when. ΔG_(a) is applied, whereby A=applied voltage via apotentiostat, and, whereby the PECO device may include a referenceelectrode (not pictured).

FIG. 2 shows one embodiment of the PECO device of the present inventionbeing a cylindrical flow-through configuration, whereby the device mayalso be referred to as a photoelectrocatalytic cell.

FIG. 3 is a graphical illustration of a nitrogen cycle for conventionalbiofiltration systems.

FIG. 4 is another illustration of photoelectrocatalytic oxidation(General for PCO).

FIG. 5 is a graph showing photocurrent generation as a function ofapplied potential demonstrating flat band potential of the instantTiO₂-coated Ti composite photoanode (“composite photoanode”) at variousinitial pH values (pH 4, pH 7 and pH 10) in NaCl solution (4 g/L),whereby linear sweep Vammetry (LSV) triplicate experiment parametersincluded −1.0 to +1.0 V vs SCE, scan rate 20 mV/s, scan increment of 2.0mV, step time 0.1 s, and, full spectrum light intensity at 1 W/cm², andwhereby control experiments without irradiation produced no currentgeneration.

FIG. 6 is a graph showing ammonia-nitrogen removal as a function of NaClconcentration (0, 0.001, 0.1, 0.25, 1 and 31 g/L) (initial pH 7) usingthe instant PECO device shown in FIG. 1, whereby triplicatechronoamperometry experiments were conducted, whereby the initialconcentration of NH₄ ⁺ was 0.54 mg/L, whereby the applied potential was+1.0 V vs SCE, and, whereby the composite photoanode was irradiated withfull spectrum light intensity at 1.09 W/cm².

FIG. 7 is a graph showing ammonia-nitrogen removal at various lightintensities (1.09, 0.60, 0.30 and 0.06 W/cm²) using the instant PECOdevice shown in FIG. 1, whereby the initial concentration of NH₄ ⁺ was0.54 mg/L in 31 g NaCl/L (initial pH 7) (triplicate experiments),whereby full spectrum light was applied, and, whereby the appliedpotential was +1.0 V vs SCE. The amount of byproducts generated duringthis test is shown in Table 2.

FIG. 8 is a graph showing ammonia removal from freshwater using theinstant PECO device shown in FIG. 1, whereby deionized freshwater (pH7.4) was spiked with 5 mg/L ammonium chloride, whereby controlconditions were the same as the experimental conditions except thatphotoanode illumination and electric potential were not applied, wherebyreplicate experiments were performed (N=2 for the controls and N=3 forthe experimental), whereby the data shown are the means±standard errorof the mean, and whereby the y-axis is the percent of the initialammonia concentration that remains in the solution at the time shown.

FIG. 9 is a graph showing ammonia removal from salt water using theinstant PECO device shown in FIGS. 1 and 2, whereby the y-axis is thedecimal fraction of the initial concentration of ammonia that remains inthe solution at the time shown.

FIG. 10 is a graph showing ammonia removal using the instant compositephotoanode in a static reactor at various number of applied coatings(translating into various film thicknesses) and sintering temperaturesof the nanoporous TiO₂ film, whereby the Ti photoanode supports weredip-coated 0, 3 or 5 times in a titania sol and sintered at 300° C. or500° C., whereby approximately 80 nm to 130 nm TiO₂ is deposited on thetitanium support per dip-coating, whereby the experiment was conductedin water containing 1 gram of NaCl per liter of fresh water withaeration, whereby the applied voltage was +1.0 V, whereby the data shownare mean±SEM (N=4), and, whereby the amount of ammonia remaining atgiven times during the 30-minute tests is shown. (All data reported inFIGS. 10-15 were conducted in freshwater).

FIG. 11 is a bar graph showing nitrate production using the instantcomposite photoanode in a static reactor at various film thicknesses andsintering temperatures of the nanoporous TiO₂ film, whereby the Tiphotoanode supports were dip-coated 0, 3 or 5 times in a titania sol andsintered at 300° C. or 500° C., whereby the experiment was conducted in100% fresh water (pH 7) with aeration, whereby the applied voltage was+1.0 V, and, whereby the data shown are mean±SEM (N=4).

FIG. 12 is a graph showing ammonia removal using the instant compositephotoanode in a static reactor at various film thicknesses and sinteringtemperatures of the nanoporous Pt-doped TiO₂ film, whereby the Tiphotoanode supports were dip-coated 3 or 5 times in a titania solcontaining 1% platinum (Pt) and fired at 300° C. or 500° C., whereby theexperiment was conducted in 100% fresh water (pH 7) with aeration,whereby the applied voltage was +1.0 V, and, whereby the data shown aremean±SEM (N=4).

FIG. 13 is a bar graph showing nitrate production using the instantcomposite photoanode in a static test reactor at various filmthicknesses and sintering temperatures of the nanoporous Pt-doped TiO₂film, whereby the Ti photoanode supports were dip-coated 3 or 5 times ina titania sol containing 1% platinum (Pt) and fired at 300° C. or 500°C., whereby the experiment was conducted in 100% fresh water (pH 7) withaeration, whereby the applied voltage was +1.0 V, and, whereby the datashown are mean±SEM (N=4).

FIG. 14 is a graph showing ammonia removal using the instant compositephotoanode in aerated and non-aerated (i.e., static) test reactorscontaining 100% fresh water (pH 7) at various film thicknesses ofnanoporous TiO₂, whereby the Ti photoanode supports were dip-coated 3 or5 times in a titania sol and sintered at 500° C., and, whereby theapplied voltage was +1.0 V (N=1).

FIG. 15 is a bar graph showing ammonia removal using the instantcomposite photoanode in a test reactor with stirring, air aeration,argon gas bubbling or static (control), whereby stirring wasaccomplished using a magnetic stir bar, whereby the uncoated Tiphotoanode supports were dip-coated 3 times in a titania sol andsintered at 500° C., whereby the y-axis shows the concentration ofammonia (as N) remaining in solution after 3 minutes of reaction,whereby the experiment was conducted in 100% fresh water (pH 7), wherebythe applied voltage was +1.0 V and N=1, and, whereby the y-axis isAmmonia Conc. (ppm as N).

FIG. 16 is a graph showing ammonia removal using uncoated Ti photoanodesupports fired at 500° C. theoretically converting the Ti to a rutilepolymorph in test reactors, whereby the initial ammonia concentrationwas 9 ppm ammonia as nitrogen, whereby the experiment was conducted in100% seawater with aeration, whereby the applied voltage was +1.0 V,and, whereby the data shown are the results of 2 independentexperiments.

FIG. 17 is a graph showing ammonia removal using uncoated Ti photoanodesupports fired at 500° C. in test reactors, whereby the experiment wasconducted in 100% seawater (INSTANT OCEAN) and freshwater containing 1g/L NaCl, whereby both waters were aerated, whereby the applied voltagewas +1.0 V, and, whereby the data shown are mean±SEM (N=3).

FIG. 18 is a graph showing ammonia removal using uncoated Ti photoanodesupports fired at 500° C. in test reactors at various water pH values(pH 5 and pH 10) in test reactors, whereby the experiment was conductedin freshwater containing 1 g/L NaCl, whereby the water was aerated,whereby the applied voltage was +1.0 V, whereby the data shown aremean±SEM (N=3), whereby the pH was adjusted using sodium hydroxide orhydrochloric acid as needed, and, whereby controls were conducted withUV lights on, but no applied voltage.

FIG. 19 is a graph showing ammonia removal using uncoated Ti photoanodesupports fired at 500° C. in test reactors at various applied voltageswith respect to the reference electrode (WRT Reference), whereby theexperiment was conducted in freshwater containing 1 g/L NaCl (pH 7),whereby water was aerated, whereby the applied voltage to the uncoatedTi photoanode support was 0, 0.3, 0.6, or 0.9 V WRT Reference, and,whereby the data shown are mean±SEM (N=3).

FIG. 20 is a bar graph showing nitrite and nitrate production usinguncoated Ti photoanode supports fired at 500° C. in batch test reactorsat various voltages applied between the uncoated Ti foil photoanodesupport and a silver wire reference, whereby the test solution consistedof 1.6 mg/L NH₄Cl in 1 g/L NaCl, whereby a potential difference of +1.0V was maintained between the reference electrode and the photoanode, andwhereby each point is an average of four replicate measurements.

FIG. 21 is a graph showing ammonia removal using the instant PECO deviceshown in FIGS. 1 and 2, whereby the experiment was conducted infreshwater containing 1 g/L NaCl (pH 7), whereby the water was aerated,whereby the applied voltage in the 2-electrode system was 2.2 V betweenthe anode and cathode, whereby the applied voltage in the 3-electrodesystem was 1 V between the anode and reference electrode (2.2 V betweenthe anode and cathode), and, whereby N=1.

FIG. 22 shows ammonia removal from water using the instant flow-throughPECO device shown in FIGS. 1 and 2, whereby the experiment was conductedin 100% seawater, whereby the water volume was 7 liters (pH 7), wherebythe water was aerated, whereby the applied voltage was +1 V, and wherebythe data shown are results of two independent trials.

FIG. 23 is an electrical circuit diagram of the electrical componentsused in the instant invention, whereby the electrical circuit is a powersupply that provides a user-selectable constant voltage and allows for arange of current (electrical load) varying between 0 and 500-1,000 mA,and whereby the circuit can be internally or externally driven by acomputer-based or machine-based controller to allow for pulsing thevoltage at a wave-form, frequency, and time (on/off) periods found to beoptimal per the needs of an application.

FIG. 24A is a graph showing the reduction of bisphenol-A over time asmeasured in Example 4.

FIG. 24B is a graph showing chlorine production over time as measured inExample 4.

FIG. 25A is a graph showing E. coli inactivation as measured in Example5.

FIG. 25B is a graph showing MS2 coliphage inactivation as measured inExample 5.

FIG. 26 is a graph showing the reduction of benzene, toluene, andethylbenzene over time as measured in Example 6.

FIG. 27 is a graph showing the reduction of benzene, toluene,ethylbenzene, and xylenes over time as measured in Example 6.

FIG. 28 is a graph showing the reduction of MTBE over time as measuredin Example 7.

FIG. 29 is a graph showing the reduction of gasoline constituents overtime as measured in Example 8.

FIG. 30 is a graph showing the reduction of benzene, acetone, BDM,chloroform, and chloromethane over time as measured in Example 9.

FIG. 31A is a graph showing the reduction of phenoxyacetic acid overtime as measured in Example 10.

FIG. 31B is a graph showing the concentration of chlorine as measured inExample 10.

FIG. 32 is a graph showing the reduction of phenol over time as measuredin Example 11.

FIG. 33A is a graph showing the reduction of carbamazepine over time asmeasured in Example 12.

FIG. 33B is a graph showing the concentration of chlorine as measured inExample 12.

FIG. 34A is a graph showing the reduction of triclosan over time asmeasured in Example 13.

FIG. 34B is a graph showing the concentration of chlorine as measured inExample 13.

FIG. 35 is a graph showing chlorine production as a function of NaClconcentration using a 9-watt, flow-through photoelectrocatalyticoxidation device with 7 liters of water and an applied voltage of +5volt as measured in Example 14.

While the disclosure is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and are herein described below in detail. Itshould be understood, however, that the description of specificembodiments is not intended to limit the disclosure to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the disclosure as defined by the appended claims.

DETAILED DESCRIPTION

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which the disclosure belongs. Although any methods andmaterials similar to or equivalent to those described herein may be usedin the practice or testing of the present disclosure, suitable methodsand materials are described below.

The instant invention will improve aquaculture production and increaseexport of U.S.-produced seafood products, particularly high valueproducts that are difficult to produce in developing countries such aslobsters and carnivorous fish species. The instant invention will alsoexpand recirculation aquaculture production, increase the efficiency ofagricultural production, and expand economic opportunities. Growth ofthe U.S. aquaculture industry will expand economic opportunities in therural U.S. New recirculation aquaculture facilities will begin supplyingfish to large existing markets.

The instant invention will also reduce the number and severity ofagriculture pest and disease outbreaks in aquaculture. The instantinvention will ensure access to nutritious food. Supporting thedevelopment and expansion of the U.S. aquaculture industry will enhancethe U.S. fish supply, which is a key component of a healthy diet.Growing demand for seafood products will also be satisfied by theinstant invention. The instant invention will also protect watershedhealth to ensure clean and abundant water, and protect and enhancewildlife habitat to benefit desired, at-risk and declining species.

Fish are very susceptible to ammonia and nitrite toxicity Ammoniaconcentrations as low as 0.025 mg/L (ppm) can kill some sensitive fishspecies. Some robust fish species may also die from exposure to ammoniaconcentrations as low as 0.2 to 0.5 mg/L. Nitrite concentrations as lowas 0.1 mg/L can also kill some fish species. The temperature and pH ofthe water also influences fish morbidity and survival. (Randall D etal., 2002, Ammonia toxicity in fish, Mar. Pollut. Bull. 45:17-23).

In aqueous ammonia-containing solutions, NH₄ ⁻ ions are in equilibriumwith non-ionized NH₃. The non-ionized form of ammonia, NH₃ is a potentneurotoxin to fish, and it readily diffuses across fish gill membranes.(Tomasso J, 1994, Toxicity of nitrogeneous wastes to aquacultureanimals, Rev. Fish. Sci. 2:291-314). The pK_(a) at equilibrium is 9.3,therefore, ammonia is more toxic to fish at higher pH values.

Nitrite is also highly toxic to fish. Nitrite levels as low as 0.1 mg/Lcan kill some fish specie. (Russo Ret al., 1991, Toxicity of ammonia,nitrite and nitrate to fishes, Aquaculture and water quality, eds. E.Brune & J. Tomasso, pp. 58-89). By comparison, nitrate is considerablyless toxic to fish than ammonia. However, nitrate can negatively impactfish health at levels around 40-50 mg/L. (Russo et al., 1991; and Ip Yet al., 2001, Ammonia toxicity, tolerance and excretion, Fish Physiologyeds. P. Wright & P. Anderson, pp. 109-148, Academic Press, San Diego).

The instant PECO device oxidizes a significant and substantial portionof ammonia to nitrogen gas. The instant PECO device also oxidizestrace-level organic contaminants (e.g., endocrine disrupters, PBDEs),disease-causing microorganisms (e.g., Escherichia coli), and potentialbiological and chemical threat agents (e.g., G- and V-series nerveagents, brucellosis, ricin). Photoelectrocatalytic oxidation is veryeffective at destroying pathogens in water. Photoelectrocatalyticoxidation also reduces the incidence of disease outbreaks that occur inrecirculation aquaculture systems and facilities.

Other aqueous solutions that may be treated with the PECO device includegroundwater, wastewater, drinking water, aquarium water, ballast water,and aquaculture water. Groundwater includes water that occurs below thesurface of the Earth, where it occupies spaces in soils or geologicstrata. Groundwater may include water that supplies aquifers, wells andsprings.

Wastewater may be any water that has been adversely affected in qualityby effects, processes, and/or materials derived from human activities.Wastewater may be water used for washing, flushing, or in amanufacturing process, that contains waste products. Wastewater mayfurther be sewage that is contaminated by feces, urine, bodily fluidsand/or other domestic, municipal or industrial liquid waste productsdisposed of via a pipe, sewer, or similar structure or infrastructure orvia a cesspool emptier. Wastewater may originate from blackwater,cesspit leakage, septic tanks, sewage treatment, washing water (alsoreferred to as “graywater”), rainfall, groundwater infiltrated intosewage, surplus manufactured liquids, road drainage, industrial sitedrainage, and storm drains, for example.

Drinking water includes water intended for supply to households,commerce and industry. Drinking water may include water drawn directlyfrom a tap or faucet. Drinking water may further include sources ofdrinking water supplies such as, for example, surface water andgroundwater.

Ballast water includes freshwater and seawater held in tanks and cargoholds of ships to increase the stability and maneuverability duringtransit. Ballast water may also contain exotic species, alien species,invasive species, and nonindiginous species and sediments.

Aquarium water includes freshwater, seawater, and saltwater used inwater-filled enclosures in which fish or other aquatic plants andanimals are kept. Aquarium water may originate from aquariums of anysize such as small home aquariums up to large aquariums holdingthousands to hundreds of thousands of gallons of water.

Aquaculture water is water used in the cultivation of aquatic organisms.Aquaculture water includes freshwater, seawater, and saltwater used inthe cultivation of aquatic organisms.

The contaminant may be an organism, an organic chemical, an inorganicchemical, and combinations thereof. Specifically, “contaminant” refersto any compound that is not naturally found in the aqueous solution.Also included are microorganisms that may be naturally found in theaqueous solution and may be considered safe at lower levels, but maypresent disease and/or other health problems at higher levels. In thecase of ballast water, also included are microorganisms that may benaturally found in the ballast water at its point of origin, but may beconsidered non-native or exotic species. Moreover, governmental agenciessuch as the United States Environmental Protection Agency, haveestablished standards for contaminants in water.

In one aspect, the contaminant may be an organism. In some embodiments,the organism is a microorganism. The microorganism may be at least oneof a prokaryote, a eukaryote, and a virus. The prokaryote may be, forexample, pathogenic prokaryotes and fecal coliform bacteria. Exemplaryprokaryotes may be Escherichia, Brucella, Legionella, and combinationsthereof.

In some embodiments, the contaminant may include eukaryotes. Exemplaryeukaryotes may be a protist, a fungus, or an alga. Exemplary protists(protozoans) may be Giardia, Cryptosporidium, and combinations thereof.The eukaryote may also be a pathogenic eukaryote. Also contemplatedwithin the disclosure are cysts of cyst-forming eukaryotes such as, forexample, Giardia.

In other embodiments, the contaminant may be a virus. Exemplary virusesmay be a waterborne virus such as, for example, enteric viruses,hepatitis A virus, hepatitis E virus, rotavirus, and MS2 coliphage,adenovirus, and norovirus.

The eukaryote may also include disease vectors. A “disease vector”refers to an insect, nematode, or other organism that transmits aninfectious agent. The life cycle of some invertebrates such as, forexample, insects, includes time spent in water. Female mosquitoes, forexample, lay their eggs in water. Other invertebrates such as, forexample, nematodes, may deposit eggs in aqueous solutions. Cysts ofinvertebrates may also contaminate aqueous environments. Treatment ofaqueous solutions in which a vector may reside may thus serve as acontrol mechanism for both the disease vector and the infectious agent.

In one aspect, the contaminant may include an organic chemical. Theorganic chemical may be any carbon-containing substance according to itsordinary meaning. The organic chemical may be chemical compounds,pharmaceuticals, over-the-counter drugs, dyes, agricultural pollutants,industrial pollutants, proteins, endocrine disruptors, fuel oxygenates,and personal care products. Exemplary organic chemicals may includeacetone, acid blue 9, acid yellow 23, acrylamide, alachlor, atrazine,benzene, benzo(a)pyrene, bromodichloromethane, carbofuran, carbontetrachloride, chlorobenzene, chlorodane, chloroform, chloromethane,2,4-dichlorophenoxyacetic acid, dalapon, 1,2-dibromo-3-chloropropane,o-dichlorobenzene, p-dichlorobenzene, 1,2-dichloroethane,1,1-dichloroethylene, cis-1,2-dichloroethylene,trans-1,2-dichloroethylene, dichlormethane, 1,2-dichloropropane,di(2-ethylhexyl)adipate, di(2-ethylhexyl)phthalate, dinoseb, dioxin(2,3,7,8-TCDD), diquat, endothall, endrin, epichlorohydrin,ethylbenzene, ethylene dibromide, glyphosate, a haloacetic acid,heptachlor, heptachlor epoxide, hexachlorobenzene,hexachlorocyclopentadiene, lindane, methyl-tertiary-butyl ether,methyoxychlor, napthoxamyl(vydate), naphthalene, pentachlorophenol,phenol, picloram, isopropylbenzene, N-butylbenzene, N-propylbenzene,Sec-butylbenzene, polychlorinated biphenyls (PCBs), simazine, sodiumphenoxyacetic acid, styrene, tetrachloroethylene, toluene, toxaphene,2,4,5-TP (silvex), 1,2,4-trichlorobenzene, 1,1,1-trichloroethane,1,1,2-trichloroethane, trichloroethylene, a trihalomethane,1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, vinyl chloride,o-xylene, m-xylene, p-xylene, an endocrine disruptor, a G-series nerveagent, a V-series nerve agent, bisphenol-A, bovine serum albumin,carbamazepine, cortisol, estradiol-17β, gasoline, gelbstoff, triclosan,ricin, a polybrominated diphenyl ether, a polychlorinated diphenylether, and a polychlorinated biphenyl. Methyl tert-butyl ether (alsoknown as, methyl tertiary-butyl ether) is a particularly suitableorganic chemical contaminant.

In one aspect, the contaminant may include an inorganic chemical. Asdefined herein, “inorganic chemical” includes nitrogen-containinginorganic chemicals such as, for example, ammonia (NH₃) or ammonium(NH₄) as described above, and non-nitrogen-containing inorganicchemicals. Non-nitrogen-containing inorganic chemicals include, forexample, aluminum, antimony, arsenic, asbestos, barium, beryllium,bromate, cadmium, chloramine, chlorine, chlorine dioxide, chlorite,chromium, copper, cyanide, fluoride, iron, lead, manganese, mercury,nickel, nitrate, nitrite, selenium, silver, sodium, sulfate, thallium,and zinc.

In one aspect, the contaminant may include a radionuclide. Radioactivecontamination may be the result of a spill or accident during theproduction or use of radionuclides (radioisotopes). Exemplaryradionuclides include an alpha photon emitter, a beta photon emitter,radium 226, radium 228, and uranium.

Without being bound to any single theory, it is hypothesized that thephotoelectrocatalytic oxidation device including the compositephotoanode performs photoelectrocatalytic oxidation of ammonia accordingto the following reactions (also referred to as break pointchlorination):

2Cl⁻→Cl₂+2e⁻  (I)

Cl₂+H₂O→HClO+Cl⁻+H⁺  (II)

2NH₄ ⁺+3HClO→N₂+2H₂O+5H+3Cl⁻  (III)

With the production of chlorine, it is also possible for this process toproduce chloroamine compounds.

Without being bound to any single theory, it has been hypothesized thatpurely photocatalytic oxidation systems are effective because theprocess generates hydroxy radicals. If hydroxyl radicals are alsogenerated in the instant photoelectrocatalytic oxidation process, thegenerated hydroxyl radical is a general oxidizing agent, therefore,other contaminants will also be oxidized. In particular, dissolvedorganic species are oxidized to water, carbon dioxide, and halide ionsduring photoelectrocatalytic oxidation. Dissolved metals having suitablereduction potentials are reduced and deposited/adhered to the metalcathode.

Additionally, the chlorine and hydroxyl radicals produced will move intothe bulk aqueous solution. As a result, contaminants will also bedestroyed by chlorine and hydroxyl radicals that have moved into thebulk aqueous solution.

In addition, the photoanode can also react with hydroxide ions (OH) andproduce OH radicals. The generated hydroxyl radical is a generaloxidizing agent; therefore, other contaminants will also be oxidized. Inparticular, dissolved organic species are oxidized to water, carbondioxide, and halide ions during photoelectrocatalytic oxidation.Dissolved metals having suitable reduction potentials are reduced anddeposited at the cathode.

Methods for Treating Aqueous Solutions

One particular objective of the instant invention is to usephotoelectrocatalysis as an ammonia treatment method for recirculatingaquaculture systems. While described herein as removing ammonia fromaquaculture systems, it should be understood by one skilled in the artthat photoelectrocatalysis of other contaminants can be performedsimilarly using the PECO device.

The instant invention utilizes photoelectrocatalytic oxidation, wherebya photocatalytic composite photoanode is combined with a cathode to forman electrolytic cell. When the instant composite photoanode isilluminated by UV light, its surface becomes highly oxidative. Bycontrolling variables such as chloride concentration, light intensity,pH and applied potential, the irradiated and biased TiO₂ compositephotoanode selectively oxidizes ammonia that comes into contact with thesurface, forming harmless nitrogen gas, whereby little or no othernitrogen compounds (e.g., nitrite) are formed as by-products.Application of a potential to the composite photoanode provides furthercontrol over the oxidation products.

PECO is an elegant, efficient, and economical solution to the problem ofnitrogenous waste removal from water. Nitrite and ammonia are rapidlyoxidized by PECO, and PECO uses very little energy. (Sun C C et al.,1998, Kinetics and mechanism of photoelectrochemical oxidation ofnitrite ion by using the rutile form of a TiO₂/Ti photoelectrode withhigh electric field enhancement, Industrial & Engineering ChemistryResearch 37:4207-4214; and, Kaneko M et al., 2006). PECO also producesfew, if any, secondary metabolites such as chlorine. The nanoporouselectrodes used in the instant invention are cost effective tomanufacture and operate.

The instant composite photoanode is constructed from a conductive metalelectrode being a Ti foil support coated with a thin layer (200-500 nm,hypothetical) of a titanium dioxide (TiO₂) that functions as aphotocatalyst. The TiO₂ photocatalyst is illuminated with light havingsufficient near UV energy generating highly reactive electrons and holespromoting oxidation of compounds on the anode surface. (Candal R J etal., 1998, TiO₂-mediated photoelectrocatalytic purification of water, J.Adv. Oxidat. Technol. 3:270-276; Candal R J et al., 1999,Titanium-supported titania photoelectrodes made by sol-gel processes, J.Environmental Engineering 125:906-912; Candal R J et al., 2000, Effectsof pH and applied potential on photocurrent and oxidation rate of salinesolutions of formic acid in a photoelectrocatalytic reactor, Environ.Sci. Technol. 34:3443-3451).

After the titanium support was coated with a thin film of TiO₂, thecomposite electrode was air-heated at a high temperature. The nanoporousTiO₂ film has a crystalline structure due to thermal oxidation. It isbelieved that the instant titania, when heated at 500° C., converts to acrystalline rutile polymorph structure. It is further believed that theinstant TiO₂ heated at 300° C. converts to a crystalline anatasepolymorph structure. In some PECO applications, rutile TiO₂ hassubstantially higher catalytic activity than the anatase TiO₂. RutileTiO₂ may also have substantially higher catalytic activity with respectto ammonia.

Exemplary photoanodes may be prepared by coating Ti metal foil being 15cm×15 cm×0.050 mm thickness and 99.6+% pure from Goodfellow Corp.,Oakdale, Pa., with a titania-based metal oxide. The Ti foil was cleanedwith a detergent solution, rinsed with deionized water, rinsed withacetone, and heat-treated at 350° C. for 4 hours providing an annealedTi foil. Annealing may also be conducted at higher temperatures such as500° C.

Following that pretreatment, the metal foil was dip-coated three or fivetimes with an aqueous suspension of titania at a withdrawal rate of ˜3.0mm/sec. After each application of coating, the coated foil was air driedfor 10-15 min and then dried in an oven at 70° C. or 100° C. for 45 min.After applying the final coating, the coated foil was sintered at 300°C., 400° C. or 500° C. for 4 hr at a 3° C./min ramp rate. Uncoated Timetal foil was similarly heat-treated and fired at 500° C. The Ti foilmay be dipped into suspensions of titania synthesized using methodsdisclosed in commonly-owned U.S. patent application Ser. Nos. 11/932,741and 11/932,519, which are incorporated herein by reference. Theoptimized withdrawal speed is around 21.5 cm min⁻¹. Titanium foil wasvery stable, and can also be used to make active photoelectrodes.

Modifications of the titanium foil that improve photoanode performanceinclude making holes or perforations at regular intervals in the foil(about 0.5 cm to about 3 cm spacing between the holes), and corrugatingthe foil to produce a regular wave-like pattern on the foil surface. Theheight of a corrugation “wave” is about 1 mm to about 5 mm. In oneembodiment, the foil is corrugated twice at right angles to each otherproducing a unique cross-hatched pattern on the foil surface. Thisembodiment of the photoanode has superior performance to foils with asingular wave pattern or no corrugations at all. Further, anodes haveregularly spaced perforations and a cross-hatched corrugation patternare particularly suitable.

Photocatalytic efficiency is significantly improved by applying apositive potential (i.e., bias) across the photoanode decreasing therecombination rate of photogenerated electrons and holes. The TiO₂ layeralso significantly impacts the photoelectrocatalytic properties of theanode. Once TiO₂ is applied to the support structure, it is heated to ahigh temperature producing a crystalline structure via thermaloxidation. It is hypothesized that titanium heated at 500° C. has arutile crystal polymorph structure. Titanium heated at lowertemperatures (e.g., 300° C.) has an anatase polymorph structure. In onephotoelectrocatalytic application, it has been reported that rutilefilms demonstrate significantly higher catalytic activity than anatasefilms. (Candal et al., 1999).

In particular, dissolved organic species are oxidized to water, carbondioxide (CO₂), and halide ions (e.g., Cl⁻) during PECO. Dissolved metalshaving appropriate reduction potentials are reduced and deposited on themetal cathode. Several operating parameters influence these reactions,such as current density, pH, chloride concentration, and the presence ofother anions such as SO₄ ²⁻, PO₄ ³⁻, NO₃ ⁻ and CO₃ ²⁻.

The instant PECO device also removes proteins from aquarium oraquaculture water. Dissolved organics (including proteins) canaccumulate in water and degrade water quality. Most salt water aquariaare equipped with a protein skimmer for removing dissolved organics andproteins. Such organic material often has a yellowish tint and issometimes called “gelbstoff” (German for yellow stuff). The PECO devicewas used for 45 mins to treat water spiked with a known concentration ofprotein being bovine serum albumin. No protein remained in the treatedwater.

In another experiment, water was spiked with gelbstoff collected from asaltwater aquarium. Using the instant PECO device, the gelbstoff wascompletely oxidized upon treatment overnight. The treated water was freeof gelbstoff and perfectly clear as measured using a wavelength of 600nm in a microplate spectrophotometer. Protein concentrations fell fromover 25 μg/ml to 0 in the same time.

An exemplary configuration of the flow-through PECO device of thepresent invention is shown in FIG. 2. The cylindrical flow-throughconfiguration includes a composite photoelectrocatalytic photoanode 10and a corresponding cathode 14. The photoanode 10 and cathode 14 arehouse within a housing 16. The housing 16 includes a water inlet 12 andoutlet 13. An electrical potential is applied across the cathode 14,composite photoanode 10 by an electrical power source and potentiostat18. A reference electrode 20 is in electrical communication with thepotentiostat 18. A UV light source 22 illuminates the compositephotoanode 10. In the instant device, the TiO₂ catalyst layer of thecomposite photoanode 10 strongly adheres to the Ti electrode and doesnot disperse into the solution. So, no need exists for a module toseparate the catalyst from the treated solution and/or to return thecatalyst to the contaminated water. In addition, because the hydroxylradical as well as Cl₂ are general oxidizing agents, other contaminants(besides ammonia) are oxidized. The instant PECO device is capable ofcompletely degrading contaminants in a single pass. Water flow rate isalso an important design parameter.

In an exemplary embodiment, the potential on the composite photoanode 10is held constant relative to a saturated calomel reference electrode bythe potentiostat 18, such as that available from EG&G, Model 6310. Thepotentiostat 18 is connected to the reference electrode through asemi-micro saline bridge, such as available from EG&G, Model K0065. Thesaline bridge may be disposed inside the reactor close to the compositephotoanode 10. The current passing through the PECO device may bemeasured.

The EG&G potentiostat was used to obtain data shown in FIGS. 5-9. Datashown in FIGS. 10-22 were obtained using a Princeton Applied ResearchModel VMP2/Z-01 Electrochemical Analyzer. The saline bridge was usedwith the EG&G system. A silver wire reference electrode was also used.

The instant potentiostat is a variable current source that can measure avoltage between two electrodes. The potentiostat can perform a widevariety of electrochemical functions, but the two exemplary functionalmodes are constant current and constant voltage. In constant currentmode, the potentiostat supplies a user specified current to theelectrodes. In constant voltage mode, it supplies current to theelectrodes while monitoring the voltage. It can then continually adjustthe current such that the voltage will remain constant at a userspecified value. A potentiostat can also be configured to supply pulses.

During operation of the instant PECO device, ammonia steadilydisappeared from the water as determined by the assay limits inapproximately 2.5 hrs. Zero to trace amounts of nitrite and nitrate werepresent in the 3 hr samples, which indicates that ammonia was convertedto nitrogen gas. The reaction was substantially faster in seawater (35ppt INSTANT OCEAN), whereby ammonia completely disappeared at 1.5 hrs.The faster reaction kinetics in seawater may be due to break pointchlorination because of the presence of chloride ions leading tophotoelectrocatalytic oxidation production of Cl₂, HOCl, and OCl⁻oxidizing specie in the seawater. Faster kinetics may also be due to thefreer flow of electrons in the saline water.

As shown in FIG. 5, at pH 4, pH 7 and pH 10, the photoanode generated ananodic current at applied potentials greater than −0.55 V. Thus, TiO₂has a flat band potential less than zero. As the pH of the solutionincreased from 4 to 7 to 10, the potential that generated an anodiccurrent changed from −0.55 V to −0.65 V to −0.76 V. This is an averagechange of 33 to 38 mV per pH unit rather than the expected 59 mV per pHunit, which may have been due to the electrolyte not fully equilibratingwith the photoanode surface prior to the start of an experiment.

Any temperature of liquid water is suitable for use with the instantPECO device. Preferably, the water is sufficiently low in turbidity topermit sufficient UV light to illuminate the composite photoanode.

As shown in FIG. 6, in a NaCl electrolyte of 0 g/L, no ammonia wasremoved. The NaCl solution at 0.25 g/L showed total ammonia removal in15 minutes Ammonia in a NaCl solution of 1 g/L was completely removed in5 minutes, and, ammonia was completely removed in 2.5 minutes when theNaCl concentration was increased to 31 g/L. 31 g NaCl/L is particularlyuseful for saltwater aquaculture systems, as this is the chlorideequivalent found in natural seawater (i.e., Cl⁻ concentration ˜19 g/L).Thus, chloride concentration affects the ammonia removal rate. Since noammonia removal was observed in the absence of chloride, ammonia mayhave been oxidized directly by the photoelectrochemical production ofchlorine.

As shown in FIG. 7, four intensities of light were tested to compare NH₄⁺/NH₃ removal and resultant NO₃ ⁻ and NO₂ ⁻ production: 1.09, 0.60,0.30, and 0.06 W/cm². Each level of intensity showed comparabledistribution of wavelengths of light ranging from 200-900 nm. At 0.06W/cm², 13% of initial ammonia was removed in fifteen minutes with no NO₃⁻ or NO₂ ⁻ produced. At 0.3 W/cm², total ammonia removal was observed in15 minutes with 9% of the ammonia-nitrogen converted to NO₂ ⁻, and 4%converted to NO₃ ⁻. At 0.6 W/cm², total ammonia removal was observed in15 minutes, with 3% of the ammonia-nitrogen converted to NO₂ ⁻, and 3%converted to NO₃ ⁻. At 1 W/cm², total ammonia removal was observed in 15minutes, with 1% of the ammonia-nitrogen converted to NO₂ ⁻ and 13%converted to NO₃ ⁻. Ammonia removal and resultant nitrogen speciesdepend on light intensity.

As shown in FIGS. 10 and 11, composite photoanodes prepared by sinteringthe TiO₂ film at 500° C. removed ammonia from water significantly fasterthan composite photoanodes fired at 300° C. Composite photoanodesprepared by applying three coatings of TiO₂ did not performsignificantly better than photoanodes prepared by applying five coatingsof TiO₂. As shown in FIG. 10, uncoated Ti foil supports fired at 500° C.demonstrated faster ammonia removal than coated Ti foil supports firedat 300° C. Similar reaction kinetics were observed for compositephotoanodes coated with nanoparticulate TiO₂ and sintered at 500° C.suggesting that a thin, highly catalytic, nanoporous TiO₂ film forms onthe surface of uncoated Ti when it is heated to 500° C. As shown in FIG.11, no nitrite and very little nitrate (<16% of ammonia nitrogen wasfound as nitrate nitrogen) were formed during the incubations suggestingthat the majority of the ammonia was oxidized into nitrogen gas.

As shown in FIGS. 12 and 13, composite photoanodes having a Ti foilsupport and a thin-film of TiO₂ doped with Pt and sintered at 300° C.removed ammonia from solution slightly better than undoped TiO₂ coatingssintered at the same temperature. There was an insignificant differencein ammonia removal between undoped and Pt-doped TiO₂ coatings sinteredat 500° C. There was also an insignificant difference between platinizedand non-platinized photoanodes in terms of the amount of nitrate formed.Approximately 15% of the original nitrogen as ammonia was converted intonitrogen as nitrate on average. Thus, the data suggest that there is noadvantage of using Pt-doped TiO₂ thin films over pure TiO₂ films forconverting aqueous ammonia into nitrogen gas in the instant PECO device.The Pt may have functioned as an electron sink in the photocatalyticreactions, which may be unnecessary when a bias (voltage) is applied tothe catalyst to pull off photogenerated electrons. Thus, the addition ofPt to the instant anodes would be an unnecessary additional expense inthe instant PECO device.

As shown in FIGS. 14 and 15, bubbling air into the static incubationtest reactors was advantageous for rapid ammonia removal. An experimentwas conducted to determine the mechanism of this aeration effect.Without being bound to any theory, it may be hypothesized as follows:(1) aeration disrupts a boundary layer that prevents ammonia fromreaching the anode surface, and (2) aeration provides oxygen requiredfor the reaction to occur, whereby oxygen is a likely final electronacceptor in the redox reactions occurring in the experiment.

There were four treatment groups: static control (no air, no stirring),water mixed with a magnetic stir bar, aeration with air, and, aerationwith argon gas (no oxygen present in the system). The results showefficient ammonia removal with stirring, air aeration, and argonaeration indicating that such mixing facilitates the reaction supportinghypothesis 1. The result also suggests that ammonia removal in theinstant PECO flow-through device would not be limited by the presence ofboundary layers when there is sufficient flow, preferably turbulentflow, through the device.

As shown in FIG. 17, ammonia removal was significantly faster in 100%seawater (40.5 g/L INSTANT OCEAN) compared to freshwater containing 1g/L NaCl. The data also suggest that some chloride must be present inthe water for the reaction to proceed. One possible explanation is thatchloride ions are required for the silver reference electrode to form asilver/silver chloride half-cell maintaining a proper voltage betweenthe anode and cathode. Another possible explanation is that (underphotoelectrocatalytic oxidation) ammonia is not directly oxidized on theanode surface. Instead, ammonia may be oxidized by reactive hypochloritegenerated in situ.

As shown in FIG. 18, ammonia removal rates were identical in water at pH5 and pH 10 suggesting that oxidation of ammonia is independent of pHover the range of pH values useable in almost all aquacultureapplications. The results also indicate that pH does not play asignificant role in regulating the oxidation of aqueous ammonia. Inaqueous solution, ammonia exists in equilibrium between the ionized (NH₄⁺) and the non-ionized form (NH₃) having equilibrium pK_(a) 9.3.Therefore, approximately 85% of the ammonia was in the NH₃ form at pH10, and essentially 100% in the NH₄ ⁺ form at pH 5. There was apossibility that the positively charged NH₄ ⁺ molecule might not havebeen oxidized as efficiently as the neutral NH₃ species because it wouldhave been repelled by the positive bias on the photoanode surface,however, that did not occur. Ammonia oxidation may not have occurreddirectly upon the anode surface. Instead, ammonia may have been oxidizedby a soluble reactive intermediary such as hypochlorite.

In other experiments, a potential of 1 V was shown to be highlyeffective. As shown in FIG. 19, four other applied voltages were testedbeing 0.0, 0.3, 0.6, and 0.9 V. Lower voltages may also be as effectiveas higher voltages. Commercial-scale devices are more cost-effective tooperate at lower voltages. At voltages higher than ˜1.2 V DC between theanode and cathode, water electrolysis occurs, whereby water moleculesbreak apart forming hydrogen gas (H₂) and oxygen gas (O₂). However,applied pulsed voltages greater than 1.2 V may be beneficial. Pulsingthe applied voltage may minimize water electrolysis and increase ammoniaoxidation efficiency.

No ammonia removal was observed without an applied bias. Ammonia removalwas greater at higher voltages probably because more electrons werecarried away maintaining a greater oxidative photoanode surface.Significant hydrogen gas production at the cathode was also observedindicating water electrolysis forming H₂ and O₂. Electrolysis of wateroccurs at voltages higher than 1.2 V, which was exceeded at all voltagestested because (with the Ag wire reference electrode) a voltage of 0between the reference electrode and anode translates to a voltage ofapproximately 1.2 V between the anode and cathode. Pulsing of theapplied voltage may minimize water electrolysis.

FIG. 20 shows the effect of applied voltage on nitrate removal. Theresults indicate that increasing the operating voltage increases therate of formation of nitrate until a plateau is reached around 0.3 V.The instant PECO device minimizes the formation of nitrite suggestingthat the applied voltage is preferably at least +0.6 V.

A 3-electrode system would be more expensive under aquacultureconditions. Efficacy of a 2-electrode configuration was tested. A2-electrode PECO device was tested at 2.2 V applied between thephotoanode and cathode, which corresponds to the same voltage betweenthe anode and cathode in the 3-electrode configuration (i.e., 1.2 Vhalf-cell+1 V). As shown in FIG. 21, ammonia removal rates wereessentially the same for the 2- and 3-electrode units.

As shown in FIG. 22, there was complete ammonia removal from seawaterinitially spiked with ˜0.7 ppm ammonia-nitrogen in 90 minutes using theflow-through reactor rather than the static reactors employed for theearlier tests discussed above. Commercial applications on the instantinvention may use flow-through reactors where variables such as waterflow rates through the device (i.e., photocatalyst contact time)determines reaction efficiency.

The amount and type of dissolved ions can affect the photocatalyticreaction rate, which is important to consider in designing a PECO unitfor treating ammonia in saltwater systems. The potential for generatingchlorine in seawater is an operating concern for PECO. It is importantto understand the effect of operating voltage on the chlorine generationrate as compared to the ammonia degradation rate in seawater systems.Thus, the voltage is to be optimized to minimize chlorine generationwhile providing a suitable ammonia conversion rate. If ammonia removaloccurs by breakpoint chlorination as hypothesized (see reactions I-IIIabove), an exemplary device would generate only enough chlorine to reactwith the ammonia being generated so that no chlorine would remain to besent back to the tank. Such a system would require effective real-timesensors for both chlorine and ammonia. A conventional activated carbonfilter may be employed to absorb and filter chlorine from the aquariumor aquaculture water.

Alkaline buffers, such as sodium and potassium bicarbonate, and sodiumand potassium hydroxide, may be employed to stabilize pH withoutsignificantly interfering with efficient operation of the instant PECOdevice. Various processes occur during photocatalytic andphotoelectrocatalytic oxidation that can affect the pH of the waterbeing treated. Any changes in the pH during treatment can alter thereaction kinetics. So, for aquaculture applications, pH is monitored toprotect fish health. The ApH is relatively small at low initial ammoniaconcentrations.

Other control conditions may also be optimized. For example, the lightsmay be active while the electrical potential is inactive, or theelectrical potential may be active while the lights are inactive.

Various UV light sources, such as germicidal UVC wavelengths (peak at254 nm) and black-light UVA wavelengths (UVA range of 300-400 nm), mayalso be employed. For the instant composite photoanodes, the optimallight wavelength for driving photoelectrocatalytic oxidization is 305nm. However, various near-UV wavelengths are also highly effective. Bothtypes of lamps emit radiation at wavelengths that activatephotoelectrocatalysis. The germicidal UV and black light lamps arewidely available and may be used in commercial applications of theinstant PECO device.

The intensity (i.e., irradiance) of UV light at the photoanode may bemeasured using a photometer available from International Light Inc.,Model IL 1400A, Super-Slim probe. An exemplary irradiation is greaterthan 3 m Wcm².

UV lamps also have a “burn-in” period. UV lamps have a limited life inthe range of approximately 6,000 to 10,000 hours. UV lamps alsotypically lose 10 to 40% of their initial lamp irradiance over thelifetime of the lamp. Thus, it is important to consider theeffectiveness of new and old UV lamps having >5,000 hrs burn-in periodlamps in designing and maintaining oxidation of ammonia.

Methods of Environmental Remediation

Another aspect of the present disclosure is directed to methods ofenvironmental remediation. “Environmental remediation” is used accordingto its ordinary meaning to refer to the removal of contaminants fromenvironmental media such as, for example, soil, groundwater, sediment,and surface water for the general protection of human health and theenvironment. The methods include providing a sample of an environmentalmedium including contaminants and exposing the sample of anenvironmental medium to photoelectrocatalytic oxidization as describedabove.

The disclosure will be more fully understood upon consideration of thefollowing non-limiting Examples.

EXAMPLE 1

Static test system. The photoanode was rolled into the cylinder anddisposed into a 300 ml glass beaker. The UV light source contained in aquartz sleeve (32 mm ID, 35 mm OD, 15 cm long) was disposed in thecenter of the beaker. The cathode (which was the counter electrode)comprised a Ti wire (0.5 mm diameter and 15 cm long from GoodfellowCorp., Oakdale, Pa.). The reference electrode comprised a silver wire(0.5 mm diameter and 15 cm long from Goodfellow Corp., Oakdale, Pa.).

The cathode and reference electrodes were attached to the outer wall ofthe quartz sleeve with silicon glue running parallel and separated by 2cm. The light source was a 9-watt, low-pressure mercury vapor lamp (JeboCorp., Taiwan, China) that emitted ultraviolet germicidal irradiation(UVGI) at a primary wavelength of 254 nm. The distance from the light tothe photoanode was approximately 5 cm. Four identical static PECOsystems were prepared for replicate testing.

Each experiment, except the 2-electrode experiment, were performed usinga 3-electrode configuration being a photoanode, a cathode, and areference electrode. In 3-electrode configuration, a potentiostatcontrolled the voltage applied to the photoanode with respect to areference electrode. A silver wire was used as the reference electrode,which functioned as a Ag/AgCl half cell in water containing chlorideions. Where relevant, voltages are reported with respect to the silverwire reference. In the 3-electrode configuration, the actual voltagebetween the photoanode and the cathode 1.2 V higher than the reportedvoltage.

Experiment procedure. The beakers were filled with 250 ml of either 100%seawater (made using 40.5 g/L of INSTANT OCEAN from Spectrum Brands,Inc., Madison, Wis.) or freshwater containing 1 g/L NaCl. Each water wasspiked with ammonium chloride to provide the ammonia source (0.5 to ˜10mg/L initial concentration). The wetted area of each photoanode wasapproximately 180 cm². In several experiments, air was bubbled into eachbeaker providing aeration and assuring uniform mixing of the waterduring the experiments using a small aquarium diaphragm air pump. Eachexperiment was conducted at room temperature (22°±2° C.).

The electrodes were connected to a Model VMP2 multi-channel potentiostatfrom Princeton Applied Research, Oak Ridge, Tenn. During operation, aconstant voltage was applied between the photoanode (the workingelectrode) and the reference electrode. The potentiostat was controlled(and the data on voltage and current were recorded) using EC-Lab V.92software from Princeton Applied Research, Oak Ridge, Tenn. Experimentswere started by simultaneously turning on both the UV lights and appliedvoltage

At set intervals every 2-5 minutes, 1-ml samples of water were collectedfrom each beaker and the ammonia concentrations were measured. Sampleswere collected in 1.5 ml microcentrifuge tubes and measured within 1 hror stored at 4° C. for later measurement. No change was observed inammonia or nitrate concentrations for up to one week of storage.

Larger samples (˜10 ml) were collected at the end of each experiment tomeasure nitrite and nitrate concentrations. These samples were stored at4° C. for later measurement. Experiments lasted several minutes or 1-4hr. 100% ammonia removal and duration depended upon the experimentalconditions being evaluated. Ammonia removal required both UV light andapplied voltage. Controlled incubations also included devices havinglight and no applied voltage.

Ammonia concentrations were measured using the indophenol method (Tetrakits) modified for use with a microtitre plate spectrophotometer.Ammonia test reagents were obtained from Tetra of Blacksburg, W.V.Nitrite and nitrate concentrations were measured using ionchromatography from Dionex of Sunnyvale, Calif.

Flow-through PECO test device. A flow-through PECO device was fabricatedby modifying a commercially available 9-watt UV sterilizer from JeboCorp., Taiwan, China. Regarding the device components for the staticsystem, a titanium wire was spot-welded to the back of the photoanodeproviding an electrical connection. The device was connected to a7-liter aquarium and water was pumped through the system with anaquarium power head at constant flow rate of 2 gallons per hour. As withthe static experiments, water samples were collected at regularintervals and ammonia concentrations were measured calorimetrically.

EXAMPLE 2

Chemicals. TiO₂ coatings on photoanodes were made from titaniumisopropoxide (Aldrich Chemical, 97%) and nitric acid (Aldrich Chemical,American Chemical Society reagent grade). NH₄Cl and NaCl were obtainedfrom Fisher Scientific (Fairlawn, N.J.). NaNO₃ and NaNO₂ standards wereobtained from SPEX Certiprep (Metuchen, N.J.). NH₄ ⁺/NH₃ was measuredusing commercial kit reagents for indophenol method. All chemicals wereused without further purification. All solutions were prepared withultrapure water (18.1 Mω cm) from a NANOpure UV system (model 07331,Bamstead/Thermolyne, Dubuque, Iowa).

Composite Photoanode Preparation. The photoanode substrate material wasannealed titanium foil 0.05 mm thick (99.6+% purity, GoodfellowCambridge Ltd). Foils were cut to size for the experimental cell andpre-heated to remove organic contaminants by firing for 300° C. for 3 h.Suspensions of titanium dioxide were prepared using processing methods.(See Candal et al., 1998). Photoanodes were dip-coated into the TiO₂suspension to achieve homogenous coatings of TiO₂ on titanium metalsupport. Two additional dip-coatings were applied, and the resultingmaterials were fired at 400° C. for 3 h to sinter the TiO₂ coating tothe Ti support.

Experimental Setup. The reaction vessel was a rectangular Teflon blockmeasuring 15.6 cm high and 7.8×8 cm, and having a single cylindricalcavity measuring 5.1 cm in diameter providing a single-compartment cell.A 4.3 cm diameter hole was cut through one side of the cell and coveredwith a quartz window. Light was passed through the window to irradiatethe photoanode. Light was generated by a 500 W Oriel brand Hg(Xe) lamp(Lamp Housing Model No. 66021, Power Supply Model 8540, Lamp Model No.66142, Newport Stratford, Conn.). Light was measured with anInternational Light IL 1700 research photometer with aSED033/QNDS2W/detector. Distribution of wavelengths (200-900 nm) wasmeasured by an Ocean Optics USB2000™ probe and OOI Base31™ software,version 2.0.1.4.

To prevent heating of the electrolyte, infrared radiation was absorbedby a water filter. Electrolyte was mixed by a stir bar and magnetic stirplate. Compressed air was slowly bubbled into solution. There was noobserved loss of electrolyte volume during the fifteen experiments. Thecell was left unsealed and exposed to room air. Each experiment employeda saturated calomel electrode (SCE) with a VYCOR frit and a bridge tubefilled with 3M KCl filling solution (Princeton Applied Research-Ametek,Oak Ridge, Tenn.).

Ammonia solution was freshly prepared before each experiment. The pH ofthe solution was adjusted with 0.1M NaOH and/or 0.1M H₂SO₄. During eachexperiment, 1.3 mL samples were periodically withdrawn for NH₄ ⁺/NH₃measurement. For the determination of NO₂ ⁻ and NO₃ ⁻, 1.3 mL sampleswere taken at the start and end of every experiment. With the exceptionof the flow-through experiments, all samples were taken from thesolution in the cell, from the irradiated side of the photoanode, anddrawn from the top of the solution using a 1-5 mL pipette withdisposable pipette tips. For experiments using the flow-through set-up,samples were taken from the 4 L reservoir. All samples were stored at 4°C. until analyzed. To control the potential during these studies, and tomeasure the photocurrent generated, an electrochemical impedanceanalyzer was used (Princeton Applied Research-Ametek, Oak Ridge, Tenn.)along with PERKINELMER Model 250 Research Electrochemistry Software(PerkinElmer, Waltham, Mass.).

Analytical Methods. The pH was measured using pH electrode (model8272BN; Thermo Orion, Beverly, Mass.) and model 370 Thermo Orion pHmeter (Thermo Orion, Beverly, Mass.). Ammonia was measured by thephenate method (APHA-AWWA-WPCE, 1985), using a spectrophotometer (λ=600nm) with a 96-well microplate autoreader (model EL311, BioTekInstruments, Winooski, Vt.). Results were analyzed with DeltaSoft3version 2.26 software (Hillsborough, N.J.).

NO₃ ⁻ and NO₂ ⁻ concentrations were measured using a Dionex ionchromatograph (IC) with an Ion Pac AG9-HC guard column (4×50 mm), and anIon Pac AS9-HC analytical column (4×250 mm) connected to an ED 50conductivity detector. An AS 40 autosampler and GP 50 gradient pump werealso used, with a sample loop volume of 200 μL.

NO₃ ⁻ and NO₂ ⁻ levels were calculated using a five-point calibrationcurve. NH₄ ⁺/NH₃ was measured using a six-point calibration curve. Bothmeasurements used external standards, with a blank sample and/orinternal standard re-checked every 20 samples. Samples were run induplicate with duplicates differing from one another less than 5%.

For all concentrations of NaCl tested, less than 4% of the ammonia wasconverted to NO₂ ⁻. (See Table 1). NO₃ ⁻ formation depended on NaClconcentration, whereby the following relationship between NaClconcentration and percentage of NO₃ ⁻ formed was observed: NaCl at 0g/L→5% NO₃ ⁻ formed; NaCl at 0.001 g/L→1% NO₃ ⁻ formed; NaCl at 0.1g/L→26% NO₃ ⁻ formed; NaCl at 0.25 g/L→41% NO₃ ⁻ formed; NaCl at 1g/L→40% NO₃ ⁻ formed; and, NaCl at 31 g/L→13% NO₃ ⁻ formed. (See Table1).

TABLE 1 Table 1. Ammonia-nitrogen removal and product yields atdifferent chloride concentrations: 0, 0.001, 0.1, 0.25, 1, and 31 gNaCl/L. Initial concentration NH₄ ⁺0.54 mg/L; initial pH 7; reactiontime 15 mins; applied potential +1.0 V vs SCE, TiO₂-coated Ti photoanodeirradiated with full spectrum light intensity 1.09 W/cm². % NH₄ ⁺ % NO₂⁻ % NO₃ ⁻ % mass NaCl (g/L) remaining yield^(a) yield^(b) recovery^(c) 0102 4 5 111 0.001 91 BDL^(d) 1 92 0.1 74 BDL^(d) 26 100 0.25 BDL^(d) 341 44 1 BDL^(d) 3 40 43 31 BDL^(d) BDL^(d) 3 13 ^(a)[NO₂ ⁻]^(t)/[NH₃]T,0 × 100. ^(b)[NO₃ ⁻]^(t)/[NH₃]T, 0 × 100. ^(c)([NO₂ ⁻]_(t15) + [NO₃⁻]_(t15) + [NH₄ ⁺]_(t15))/[NH₄ ⁺]_(t0) × 100. ^(d)Below detectionlimits.

TABLE 2 Table 2. Ammonia removal and product yields at different lightintensities: 1.09, 0.60, 0.30, and 0.06 W/cm². Initial concentration NH₄⁺ 0.54 mg/L; initial pH 7; reaction time 15 mins; applied potential +1.0V vs SCE, TiO₂-coated Ti photoanode irradiated with full spectrum light.Light Intensity % NH₄ ⁺ % NO₂ ⁻ % NO₃ ⁻ % mass (W/cm²) remainingyield^(a) yield^(b) recovery^(c) 0.064 87 BDL^(d) BDL^(d) 87 0.3 BDL^(d)9 4 13 0.6 BDL^(d) 3 3 6 1 BDL^(d) 1 13 14 ^(a)[NO₂ ⁻]^(t)/[NH₃]T, 0 ×100. ^(b)[NO₃ ⁻]^(t)/[NH₃]T, 0 × 100. ^(c)([NO₂ ⁻]_(t15) + [NO₃⁻]_(t15) + [NH₄ ⁺]_(t15))/[NH₄ ⁺]_(t0) × 100. ^(d)Below detectionlimits.

EXAMPLE 3

Fifteen minute chronoamperometry experiments were conducted to analyzethe effects of salinity, light intensity, and applied potential on thephotoelectrocatalytic oxidation of aqueous NH₄ ⁺/NH₃. TiO₂ coatings wereapplied to Ti foil by dip coating and sintered at 400° C. to sinter ananoporous photocatalytic surface. Photoanodes were used in combinationwith a platinum wire counter electrode and saturated calomel referenceelectrode (SCE) to test ammonia removal and nitrate/nitrite productionat initial ammonium/ammonia concentration 0.54 mg NH₄ ⁺/L, initial pH 7in a well-mixed static reactor with compressed air sparged intosolution. At applied potentials greater than −0.4 V, NH₄ ⁺ was totallyremoved in ten minutes and less than 3% of the initial NH₄ ⁺ wasconverted to NO₃ ⁻ and none was converted to NO₂ ⁻.

Chloride ions are present at 0.25 g NaCl/L or greater so that ammoniaoxidation occurs. Conversion of NH₄ ⁻ and NO₃ to N₂ reached 40-41% atlower salinities, but at 31 g NaCl/L, only 3% of NH₄ ⁺—N was convertedto NO₃ ⁻N. No more than 4% of NH₄ ⁺—N was converted to NO₂—N for anysalinity tested. At least 0.3 W/cm² is applied for NH₄ ⁺ oxidation, and9% or less of the initial NH₄ ⁺—N formed NO₃ ⁻—N or NO₂—N.

EXAMPLE 4

In this Example, the removal of bisphenol-A using the methods describedherein was analyzed over time. Water samples including 100 μg/Lbisphenol A, 20 ppt NaCl, and Milli-Q water (4 L total volume) werecollected for analysis in vials containing 100 μl H₂SO₄ and 100 μlsodium thiosulfate (300 mg/L). H₂SO₄ serves as a preservative and sodiumthiosulfate neutralizes residual oxidants in the sample to preventcontinued oxidation in the sample vial.

Samples were treated using a 9-watt photoelectrocatalytic oxidationdevice (PECO) as described herein. Control samples were treated by (1)UV light and no applied potential (data shown); (2) no UV light and noapplied potential; and (3) no UV light with applied potential. Waterflow rate was 3.5 L/min. Levels of bisphenol-A was measured using liquidchromatography/mass spectrometry (LC/MS). The DPD(N,N-diethyl-p-phenylenediamine) method was used for measuring chlorine.

Bisphenol-A was reduced to undetectable levels. FIG. 24A shows thereduction of bisphenol-A and FIG. 24B shows the concentration ofchlorine over time. Table 3 summarizes results.

TABLE 3 Time Chlorine Current (min.) Control PECO (mg/L) (mA) 0 0.2530.212 0.0 20 5 0.226 0.194 0.0 29 10 0.251 0.193 0.0 20 15 0.246 0.1920.2 19 20 0.205 0 0.3 18 25 0.203 0 0.3 18 30 0.199 0 0.3 18 35 0.198 00.3 18 40 0.22 0 0.3 18 45 0.209 0 0.3 19 50 0.194 0 0.3 19 55 0.202 00.4 19 60 0.189 0 0.4 19 85 0.193 0 0.5 19

EXAMPLE 5

In this Example, the inactivation of Escherichia coli (E. coli) and MS2coliphage using the methods described herein was analyzed over time. ForE. coli inactivation, a recirculation batch system using a 36-watt PECOdevice, a 10 L glass aquarium filled with 5 L of de-chlorinated (100mg/L chloride concentration) tap water, and a small aquarium pump wasspiked with E. coli (ATCC 11775) at a concentration of ˜3×10⁸ cells/ml.The PECO device was activated and water samples were collected every 10minutes for one hour. Results were obtained by enumerating on R2A agarand incubating for 24 hours at 37° C. Free chlorine was measured using aDPD colorimetric assay according to Standard Methods 4500. For theinactivation of MS2 coliphage, a recirculation batch system using a36-watt PECO device, a 7-L glass aquarium filled with 4 L of ultrapurewater containing 165 mg/L of NaCl (100 mg/L of chloride) was spiked withMS2 coliphage (ATCC 15597-B 1). MS2 spike preparations were madeaccording to Long and Sobsey (2004). Enumeration results were plotted aslog inactivation versus time, where log inactivation is defined as thebase 10 log of the final microbial concentration divided by the initialconcentration.

As shown in FIG. 25A, levels of E. coli in samples treated usingphotoelectrocatalytic oxidation decreased by over 6 log (99.9999%) inless than 10 minutes, whereas levels of E. coli in the sample treatedwith the 36-watt UV sterilizer decreased to a level of approximately 4log over 1 hour. Levels in control (no PECO, no UV) remained constant.Chlorine production rate increased by 68% with an increase in flowvelocity from 6 to 18 m/min. Chlorine production rate increased by 63%with an increase in space-time from 2.4 to 7.3 mg*min/mol.

As shown in FIG. 25B, 1-log inactivation of MS2 coliphage occurred after5.2 minutes, 2-log inactivation occurred after 10.4 minutes, and 3-loginactivation occurred after 15.5 minutes. The maximum detectableinactivation was 6.7-log inactivation.

EXAMPLE 6

In this Example, the removal of various organic chemicals from anaqueous solution using the methods described herein was analyzed overtime. Specifically, benzene, toluene, ethylbenzene, and xylenes (BTEX)using a 36-watt photoelectrocatalytic oxidation device (PECO) wasanalyzed. Samples were prepared using 1.2 L of tap water spikedgasoline. Samples were collected at time intervals following PECO andconcentrations of BTEX chemicals were analyzed by GC/MS. Control sampleswere treated by (1) UV light and no applied potential; (2) no UV lightand no applied potential; and (3) no UV light with applied potential.

As shown in FIG. 26 and FIG. 27, benzene, toluene, ethylbenzene, and m-and p-xylenes were reduced to undetectable levels. o-Xyleneconcentration was also reduced over time. Table 4 summarizes the resultsof the experiment including m-, p-, and o-xylenes.

TABLE 4 m- and p- Time Benzene Toluene Ethylbenzene Xylenes o-Xylene(min.) (ppb) (ppb) (ppb) (ppb) (ppb) 0 4 5 1 69 47 15 2 1 0 21 34 30 1 00 1 18 45 1 0 0 0 12 60 0 0 0 0 9

EXAMPLE 7

In this Example, the removal of gasoline constituents using the methodsdescribed herein was analyzed over time. Specifically, MTBE, THF,acetone, toluene, EB, oxylene, and 1,3,5-TMB were treated using the 36Watt PECO device of Example 6. Lake water (i.e., a complex water matrix)was mixed with regular grade gasoline to form a surrogate contaminatedgroundwater sample. The sample was then stored for approximately onemonth prior to treatment. Twenty five gallons of the sample was treatedby four (4) 36-watt PECO units connected in series in recirculationbatch mode at a flow rate of 18 gpm. Samples were collected at regularintervals and concentrations of volatile organic compounds were analyzedby GC/MS.

As shown in FIG. 28, MTBE was removed over time. THF was also removedover time. Table 5 summarizes the results for MTBE, THF, acetone,toluene, EB, oxylene, and 1,3,5-TMB.

TABLE 5 Ace- 1,3,5- Time MTBE THF tone Toluene Ethylbenzene Oxylene TMB(min) (ppb) (ppb) (ppb) (ppb) (ppb) (ppb) (ppb) 0 360 20 0 0 0 0 0 15310 18 0 0 0 0 0 30 270 15 4 0 0 0 0 45 190 13 8 0 0 0 0 60 160 11 10 00 1 0 150 50 7 40 2 1 8 2

EXAMPLE 8

In this Example, the removal of gasoline constituents over time usingthe methods described in Example 7 was analyzed.

FIG. 29 shows the removal of toluene, ethylbenzene,1,3,5-trimethylbenzene, and isopropylbenzene at time points of 0 and 1hour. Table 6 summarizes the results for toluene, xylenes, benzene,ethylbenzene, 1,2,4-trimethylbenzene, napthlyene,1,3,5-trimethylbenzene, N-propylbenzene, N-butylbenzene,isopropylbenzene, 1,2-dichloroethane, Sec-butylbenzene, acetone,bromodichloromethane, chloroform, and chloromethane.

TABLE 6 Chemical Time 0 Time 1 h Toluene 320 20 Xylenes 257 11.7 Benzene130 11 Ethylbenzene 45 2.3 1,2,4-trimethylbenzene 44 2.5 Napthlyene 133.8 1,3,5-trimethylbenzene 13 1.4 N-propylbenzene 5.2 0 N-butylbenzene3.5 0 Isopropylbenzene 3.1 2 1,2-dichloroethane 2.1 0 Sec-butylbenzene1.7 0 Acetone 0 8.5 Bromodichloromethane 0 7.6 Chloroform 0 42Chloromethane 0 1.5

EXAMPLE 9

In this Example, the removal of benzene over time using the methodsdescribed in Example 7 was analyzed. Benzene concentration was reducedas shown in FIG. 30. Table 7 summarizes the results for benzene,acetone, BDM, chloroform, and chloromethane.

TABLE 7 Benzene Acetone BDM Chloroform Chloromethane Time (hr) (μg/L)(μg/L) (μg/L) (μg/L) (μg/L) 0 15 2 13 4 5.2 32 11 9.7 1.4

EXAMPLE 10

In this Example, the removal of sodium phenoxyacetic acid (phenoxyaceticacid) using the methods described herein was analyzed over time. Asample was prepared using 100 μg/L initial sodium phenoxyacetic acid, 20ppt NaCl, and Milli-Q water (4 L total volume). Samples were collectedat regular intervals in 40 ml vials containing 100 μl H₂SO₄, and 100 μlsodium thiosulfate (300 mg/L). Samples were treated using the 9-wattPECO device of Example 4. Control samples were treated by (1) UV lightand no applied potential (data shown); (2) no UV light and no appliedpotential; and (3) no UV light with applied potential. The DPD(N,N-diethyl-p-phenylenediamine) method was used for measuring chlorine.

FIG. 31A shows the reduction of phenoxyacetic acid over time and FIG.31B shows the concentration of chlorine. Table 8 summarizes the results.

TABLE 8 Time Current Chlorine Control PECO (min.) (MA) (mg/L) ControlPECO (%) (%) 0 0 0.0 805.0 558.0 100.0 100.0 5 0 0.0 780.0 501.0 96.989.8 10 0 0.0 756.0 441.0 93.9 79.0 15 0.0 0.0 661.0 388.0 82.1 69.2 200 0.0 661.0 353.0 82.1 63.3 25 0 0.0 613.0 335.0 76.1 60.0 30 0 0.0542.0 299.0 67.3 53.6 35 0 0.0 535.0 245.0 66.5 43.9 40 0 0.0 549.0243.0 68.2 43.5 45 0 0.0 552.0 210.0 68.6 37.6 50 0 0.0 538.0 177.0 68.831.7 55 0 0.0 513.0 147.0 63.7 26.3 0 0 0.0 517.0 133.0 64.2 23.8

EXAMPLE 11

In this Example, the removal of phenol using the methods describedherein was analyzed over time. A sample was prepared using 10 μg/Linitial phenol, 20 ppt NaCl, and Milli-Q water (4 L total volume).Samples were treated using the 9-watt PECO device of Example 4. Controlsamples were treated by (1) UV light and no applied potential (datashown); (2) no UV light and no applied potential; and (3) no UV lightwith applied potential.

FIG. 32 shows the removal of phenol over time. Table 9 summarizes theresults.

TABLE 9 Time (min.) Control (μg/ml) Phenol (μg/ml) 0 8.42 7.97 10 8.426.4 20 6.81 7.4 30 6.82 7.4 40 6.92 6.4 50 6.71 5.9 60 7.49 5.2 70 7.994.8 80 6.55 4.2 90 7.23 4.4 100 7.50 3.9 110 7.08 3.7 120 7.02 3.4 1506.39 2.9 180 6.5 2.5

EXAMPLE 12

In this Example, the removal of carbamazepine using the methodsdescribed herein was analyzed over time. A sample was prepared using 100μg/L (100 ppb) initial carbamazepine, 20 ppt NaCl, and Milli-Q water (4L total volume). Samples were treated using the 9-watt PECO device ofExample 4. Control samples were treated by (1) UV light and no appliedpotential (data shown); (2) no UV light and no applied potential; and(3) no UV light with applied potential.

FIG. 33A shows the removal of carbamazepine over time and FIG. 33B showsthe concentration of chlorine. Table 10 summarizes the results.

TABLE 10 Time Current Chlorine Carbamazepine PECO PECO (min.) (mA)(mg/L) Control (rep. 1) (rep. 2) 0 26 0.0 76.5 78.2 76.9 5 29 0.2 76.547.1 52.6 10 20 0.3 78.3 6.9 18.3 15 20 0.3 77.4 0.0 1.4 20 21 0.4 76.30.0 0.0 25 21 0.5 75.9 0.0 0.0 30 21 0.5 73.5 0.0 0.0 35 21 0.6 73.5 0.00.1 40 21 0.6 76.4 0.0 0.0 45 22 0.7 74.4 0.0 0.0 50 22 0.8 76.3 0.0 0.055 22 0.8 74.7 0.0 0.0 60 22 0.8 76.5 0.0 0.0

EXAMPLE 13

In this Example, the removal of triclosan using the methods describedherein was analyzed over time. A sample was prepared using 20 μg/Linitial triclosan, 20 ppt NaCl, and Milli-Q water (4 L total volume).Samples were treated using the 9-watt PECO device of Example 4. Controlsamples were treated by (1) UV light and no applied potential (datashown); (2) no UV light and no applied potential; and (3) no UV lightwith applied potential.

FIG. 34A shows the removal of triclosan over time and FIG. 34B shows theconcentration of chlorine. Table 11 summarizes results.

TABLE 11 Triclosan Time Current Chlorine Control PECO PECO (min.) (mA)(mg/L) (ng/ml) (rep. 1) (rep. 2) 0 23 0.0 18.4 16.9 15.0 5 22 0.0 15.51.0 2.7 10 22 0.1 14.1 0.0 0.1 15 22 0.0 13.0 0.0 0.0 20 22 0.1 12.2 0.10.1 25 22 0.3 10.8 0.0 0.0 30 22 0.4 9.9 0.0 0.0 35 22 0.5 9.5 0.0 0.040 22 0.7 8.7 0.0 0.0 45 22 0.6 7.6 0.0 0.0 50 22 0.8 7.6 0.0 0.0 55 230.9 6.9 0.0 0.1 60 23 0.9 6.2 0.1 0.0

EXAMPLE 14

In this Example, methyl tertiary-butyl ether is removed fromsynthetically prepared MTBE-spiked water samples and MTBE contaminatedgroundwater. For synthetically prepared MTBE-spiked water samples,reagent-grade MTBE (97%, Sigma Aldrich Chemical Co., Milwaukee, Wis.) isused to prepare a stock solution of 1000 mg/L MTBE in deionized water.The reaction solutions are prepared by diluting the 1000 mg/L MTBE stocksolution to the desired MTBE concentration with deionized oxygenatedwater. The water is oxygenated to permit the measurement of totalorganic carbon (TOC) with minimal interference from dissolved CO₂ in thesamples. Water contaminated with MTBE is kept in airtight Pyrex flaskswith no headspace at the onset of the reaction to avoid MTBEvolatilization.

Effect of Salt Concentration on MTBE Removal

The effect of NaCl concentration on the degradation of MTBE at aninitial concentration of 500 μg/L is evaluated. The following NaClconcentrations are tested: 1, 2, 5, 10 and 20 g/L. These NaClconcentrations are tested because of their differing effects on chlorinegeneration by a 9-watt PECO device as shown in FIG. 35. MTBE and itsexpected by-products are measured by GC-MS for each NaCl concentration.Chlorine production is also measured.

Effect of Initial MTBE Concentration

The effect of initial MTBE concentration on degradation efficiency andorder of reaction is performed. Initial MTBE concentrations of 1 μg/L,10 μg/L, 100 μg/L, 1 mg/L, and 10 mg/L are used. Photoelectrocatalyticoxidation is performed until complete mineralization is achieved asmeasured by TOC. MTBE and its by-products are determined by GC-MS. Rateconstants are estimated by assuming that the system followspseudo-first-order kinetics (i.e., from the slopes of the lines producedby plotting −ln (C/C₀) versus time). Other kinetic rate models,including zero- and second-order power-law kinetics models, as well asLangmuir-Hinshelwood expressions, are analyzed to determine if thesemodels provide better fits to the data.

Effect of Competing Organic Compounds on MTBE Removal

MTBE-contaminated groundwater samples are evaluated to determine theimpact of competing contaminates in the water on MTBE removal kinetics.The groundwater samples are analyzed in triplicate photoelectrocatalyticoxidation units until there is complete mineralization of all compoundsin the water. The levels of MTBE, its by-products, and BTEX compoundsare measured at each time point.

1. A method of treating an aqueous solution to reduce amounts of acontaminant, the method comprising: providing an aqueous solutioncomprising at least one contaminant selected from the group consistingof an organism, an organic chemical, a non-nitrogen inorganic chemical,and combinations thereof; and exposing the aqueous solution tophotoelectrocatalytic oxidization, wherein one or more contaminant isoxidized by a free radical produced by a photoanode, wherein thephotoanode comprises an anatase polymorph of titanium, a rutilepolymorph of titanium, or a nanoporous film of titanium dioxide.
 2. Themethod of claim 1, wherein the aqueous solution comprises groundwater,wastewater, drinking water, aquarium water, ballast water, andaquaculture water.
 3. The method of claim 1, wherein the aqueoussolution is groundwater.
 4. The method of claim 1, wherein the aqueoussolution is wastewater.
 5. The method of claim 1, wherein the aqueoussolution is drinking water.
 6. The method of claim 1, wherein theaqueous solution is aquarium water.
 7. The method of claim 1, whereinthe aqueous solution is ballast water.
 8. The method of claim 1, whereinthe aqueous solution is aquaculture water.
 9. The method of claim 1,wherein the free radical is at least one of a hydroxyl radical and achlorine atom.
 10. The method of claim 1, wherein the one or morecontaminant is oxidized on, or proximate to, a surface of thephotoanode.
 11. The method of claim 1, wherein the organism is amicroorganism.
 12. The method of claim 11, wherein the microorganismcomprises at least one of a prokaryote, a eukaryote, and a virus. 13.The method of claim 12, wherein the prokaryote comprises Escherichia.14. The method of claim 1, wherein the organic chemical comprises atleast one of acetone, acid blue 9, acid yellow 23, acrylamide, alachlor,atrazine, benzene, benzo(a)pyrene, bromodichloromethane, carbofuran,carbon tetrachloride, chlorobenzene, chlorodane, chloroform,chloromethane, 2,4-dichlorophenoxyacetic acid, dalapon,1,2-dibromo-3-chloropropane, o-dichlorobenzene, p-dichlorobenzene,1,2-dichloroethane, 1,1-dichloroethylene, cis-1,2-dichloroethylene,trans-1,2-dichloroethylene, dichlormethane, 1,2-dichloropropane,di(2-ethylhexyl)adipate, di(2-ethylhexyl)phthalate, dinoseb,dioxin(2,3,7,8-TCDD), diquat, endothall, endrin, epichlorohydrin,ethylbenzene, ethylene dibromide, glyphosate, a haloacetic acid,heptachlor, heptachlor epoxide, hexachlorobenzene,hexachlorocyclopentadiene, lindane, methyl-tertiary-butyl ether,methyoxychlor, napthoxamyl(vydate), naphthalene, pentachlorophenol,phenol, picloram, isopropylbenzene, N-butylbenzene, N-propylbenzene,Sec-butylbenzene, polychlorinated biphenyls (PCBs), simazine, sodiumphenoxyacetic acid, styrene, tetrachloroethylene, toluene, toxaphene,2,4,5-TP (silvex), 1,2,4-trichlorobenzene, 1,1,1-trichloroethane,1,1,2-trichloroethane, trichloroethylene, a trihalomethane,1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, vinyl chloride,o-xylene, m-xylene, p-xylene, an endocrine disruptor, protein, aG-series nerve agent, a V-series nerve agent, bisphenol-A, bovine serumalbumin, carbamazepine, cortisol, estradiol-17β, gasoline, gelbstoff,triclosan, ricin, a polybrominated diphenyl ether, a polychlorinateddiphenyl ether, and a polychlorinated biphenyl.
 15. The method of claim1, wherein the non-nitrogen inorganic chemical comprises at least one ofaluminum, antimony, arsenic, asbestos, barium, beryllium, bromate,cadmium, chloramine, chlorine, chlorine dioxide, chlorite, chromium,copper, cyanide, fluoride, iron, lead, manganese, mercury, nickel,nitrate, nitrite, selenium, silver, sodium, sulfate, thallium, and zinc.16. The method of claim 1, wherein the contaminant is methyltertiary-butyl ether.
 17. A method of environmental remediation, themethod comprising: providing a sample of environmental medium comprisingat least one contaminant selected from the group consisting of anorganism, an organic chemical, a non-nitrogen inorganic chemical, andcombinations thereof; and exposing the sample of environmental medium tophotoelectrocatalytic oxidization, wherein one or more contaminant isoxidized by a free radical produced by a photoanode, wherein thephotoanode comprises an anatase polymorph of titanium, a rutilepolymorph of titanium, or a nanoporous film of titanium dioxide.
 18. Themethod of claim 17, wherein the environmental medium comprises at leastone of groundwater and surface water.
 19. The method of claim 17,wherein the one or more contaminant is oxidized on, or proximate to, asurface of the photoanode.
 20. A method of treating an aqueous solutionto reduce amounts of a contaminant, the method comprising: providing anaqueous solution comprising at least one contaminant selected from thegroup consisting of an organism, an organic chemical, a non-nitrogeninorganic chemical, and combinations thereof; and exposing the aqueoussolution to photoelectrocatalytic oxidization, wherein one or morecontaminant is oxidized by a chlorine atom produced by a photoanode,wherein the photoanode comprises an anatase polymorph of titanium, arutile polymorph of titanium, or a nanoporous film of titanium dioxide.